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 $65.98   11.571%   $73.6145   $73.61   $73.60   $73.60  
  Purchase #2 $117.86   4.848%   $123.5739   $123.57   $123.55   $123.60  
  Purchase #3 $184.34   12.644%   $207.6479   $207.65   $207.65   $207.60  
  Purchase #4 $62.44   12.621%   $70.3206   $70.32   $70.30   $70.30  
  Purchase #5 $60.75   3.680%   $62.9856   $62.99   $63.00   $63.00  
  Purchase #6 $221.39   8.796%   $240.8635   $240.86   $240.85   $240.90  
  Purchase #7 $95.50   11.555%   $106.535   $106.54   $106.55   $106.50  
  7 purchase totals = $808.26       $885.5410   $885.54   $885.50   $885.50