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 $41.57   9.649%   $45.5811   $45.58   $45.60   $45.60  
  Purchase #2 $173.43   12.355%   $194.8573   $194.86   $194.85   $194.90  
  Purchase #3 $24.78   5.632%   $26.1756   $26.18   $26.20   $26.20  
  Purchase #4 $59.90   9.438%   $65.5534   $65.55   $65.55   $65.60  
  Purchase #5 $194.27   3.729%   $201.5143   $201.51   $201.50   $201.50  
  Purchase #6 $125.58   7.479%   $134.9721   $134.97   $134.95   $135.00  
  Purchase #7 $121.88   13.572%   $138.4216   $138.42   $138.40   $138.40  
  7 purchase totals = $741.41       $807.0754   $807.07   $807.05   $807.20