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 $94.56   4.288%   $98.6147   $98.61   $98.60   $98.60  
  Purchase #2 $126.60   9.712%   $138.8954   $138.90   $138.90   $138.90  
  Purchase #3 $116.56   5.317%   $122.7575   $122.76   $122.75   $122.80  
  Purchase #4 $182.66   12.725%   $205.9035   $205.90   $205.90   $205.90  
  Purchase #5 $31.98   12.496%   $35.9762   $35.98   $36.00   $36.00  
  Purchase #6 $179.45   11.224%   $199.5915   $199.59   $199.60   $199.60  
  Purchase #7 $60.75   5.758%   $64.248   $64.25   $64.25   $64.20  
  7 purchase totals = $792.56       $865.9868   $865.99   $866.00   $866.00