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 $22.76   7.144%   $24.386   $24.39   $24.40   $24.40  
  Purchase #2 $44.96   8.873%   $48.9493   $48.95   $48.95   $48.90  
  Purchase #3 $27.76   5.304%   $29.2324   $29.23   $29.25   $29.20  
  Purchase #4 $239.91   11.842%   $268.3201   $268.32   $268.30   $268.30  
  Purchase #5 $53.43   7.555%   $57.4666   $57.47   $57.45   $57.50  
  Purchase #6 $142.61   12.622%   $160.6102   $160.61   $160.60   $160.60  
  Purchase #7 $146.81   13.421%   $166.5134   $166.51   $166.50   $166.50  
  7 purchase totals = $678.24       $755.4780   $755.48   $755.45   $755.40