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 $235.44   13.219%   $266.5628   $266.56   $266.55   $266.60  
  Purchase #2 $220.90   10.349%   $243.7609   $243.76   $243.75   $243.80  
  Purchase #3 $19.56   8.460%   $21.2148   $21.21   $21.20   $21.20  
  Purchase #4 $115.93   8.232%   $125.4734   $125.47   $125.45   $125.50  
  Purchase #5 $179.52   10.375%   $198.1452   $198.15   $198.15   $198.10  
  Purchase #6 $68.70   3.784%   $71.2996   $71.30   $71.30   $71.30  
  Purchase #7 $25.66   8.601%   $27.867   $27.87   $27.85   $27.90  
  7 purchase totals = $865.71       $954.3237   $954.32   $954.25   $954.40