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 $58.79   6.586%   $62.6619   $62.66   $62.65   $62.70  
  Purchase #2 $110.57   12.799%   $124.7219   $124.72   $124.70   $124.70  
  Purchase #3 $158.95   9.445%   $173.9628   $173.96   $173.95   $174.00  
  Purchase #4 $195.46   11.276%   $217.5001   $217.50   $217.50   $217.50  
  Purchase #5 $56.78   3.426%   $58.7253   $58.73   $58.75   $58.70  
  Purchase #6 $73.27   8.220%   $79.2928   $79.29   $79.30   $79.30  
  Purchase #7 $25.61   11.151%   $28.4658   $28.47   $28.45   $28.50  
  7 purchase totals = $679.43       $745.3306   $745.33   $745.30   $745.40