Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.99   13.150%   $267.0227   $267.02   $267.00   $267.00  
  Purchase #2 $55.30   10.407%   $61.0551   $61.06   $61.05   $61.10  
  Purchase #3 $194.66   4.677%   $203.7642   $203.76   $203.75   $203.80  
  Purchase #4 $231.86   9.848%   $254.6936   $254.69   $254.70   $254.70  
  Purchase #5 $180.53   10.588%   $199.6445   $199.64   $199.65   $199.60  
  Purchase #6 $113.65   5.770%   $120.2076   $120.21   $120.20   $120.20  
  Purchase #7 $168.85   11.741%   $188.6747   $188.67   $188.65   $188.70  
  7 purchase totals = $1,180.84       $1,295.0624   $1,295.05   $1,295.00   $1,295.10