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 $53.91   5.838%   $57.0573   $57.06   $57.05   $57.10  
  Purchase #2 $201.58   12.196%   $226.1647   $226.16   $226.15   $226.20  
  Purchase #3 $210.50   11.190%   $234.055   $234.06   $234.05   $234.10  
  Purchase #4 $63.43   4.295%   $66.1543   $66.15   $66.15   $66.20  
  Purchase #5 $246.38   5.738%   $260.5173   $260.52   $260.50   $260.50  
  Purchase #6 $13.39   3.203%   $13.8189   $13.82   $13.80   $13.80  
  Purchase #7 $88.72   6.161%   $94.186   $94.19   $94.20   $94.20  
  7 purchase totals = $877.91       $951.9535   $951.96   $951.90   $952.10