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 $58.95   6.829%   $62.9757   $62.98   $63.00   $63.00  
  Purchase #2 $58.93   6.220%   $62.5954   $62.60   $62.60   $62.60  
  Purchase #3 $69.56   7.282%   $74.6254   $74.63   $74.65   $74.60  
  Purchase #4 $91.27   4.545%   $95.4182   $95.42   $95.40   $95.40  
  Purchase #5 $92.61   12.329%   $104.0279   $104.03   $104.05   $104.00  
  Purchase #6 $37.29   8.387%   $40.4175   $40.42   $40.40   $40.40  
  Purchase #7 $180.56   9.129%   $197.0433   $197.04   $197.05   $197.00  
  7 purchase totals = $589.17       $637.1034   $637.12   $637.15   $637.00