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 $46.82   5.483%   $49.3871   $49.39   $49.40   $49.40  
  Purchase #2 $213.80   7.421%   $229.6661   $229.67   $229.65   $229.70  
  Purchase #3 $19.72   13.809%   $22.4431   $22.44   $22.45   $22.40  
  Purchase #4 $87.98   13.124%   $99.5265   $99.53   $99.55   $99.50  
  Purchase #5 $217.52   7.141%   $233.0531   $233.05   $233.05   $233.10  
  Purchase #6 $136.31   9.838%   $149.7202   $149.72   $149.70   $149.70  
  Purchase #7 $231.76   7.505%   $249.1536   $249.15   $249.15   $249.20  
  7 purchase totals = $953.91       $1,032.9497   $1,032.95   $1,032.95   $1,033.00