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 $240.63   5.271%   $253.3136   $253.31   $253.30   $253.30  
  Purchase #2 $71.89   12.678%   $81.0042   $81.00   $81.00   $81.00  
  Purchase #3 $226.48   12.591%   $254.9961   $255.00   $255.00   $255.00  
  Purchase #4 $158.75   11.849%   $177.5603   $177.56   $177.55   $177.60  
  Purchase #5 $135.90   10.829%   $150.6166   $150.62   $150.60   $150.60  
  Purchase #6 $25.80   4.528%   $26.9682   $26.97   $26.95   $27.00  
  Purchase #7 $241.97   7.445%   $259.9847   $259.98   $260.00   $260.00  
  7 purchase totals = $1,101.42       $1,204.4437   $1,204.44   $1,204.40   $1,204.50