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 $48.66   11.751%   $54.378   $54.38   $54.40   $54.40  
  Purchase #2 $134.87   6.525%   $143.6703   $143.67   $143.65   $143.70  
  Purchase #3 $212.99   10.201%   $234.7171   $234.72   $234.70   $234.70  
  Purchase #4 $161.50   3.577%   $167.2769   $167.28   $167.30   $167.30  
  Purchase #5 $60.28   11.732%   $67.352   $67.35   $67.35   $67.40  
  Purchase #6 $75.28   4.595%   $78.7391   $78.74   $78.75   $78.70  
  Purchase #7 $158.32   4.352%   $165.2101   $165.21   $165.20   $165.20  
  7 purchase totals = $851.90       $911.3435   $911.35   $911.35   $911.40