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 $147.59   11.746%   $164.9259   $164.93   $164.95   $164.90  
  Purchase #2 $58.55   10.279%   $64.5684   $64.57   $64.55   $64.60  
  Purchase #3 $236.29   8.506%   $256.3888   $256.39   $256.40   $256.40  
  Purchase #4 $106.97   11.847%   $119.6427   $119.64   $119.65   $119.60  
  Purchase #5 $39.86   12.872%   $44.9908   $44.99   $45.00   $45.00  
  Purchase #6 $60.95   9.583%   $66.7908   $66.79   $66.80   $66.80  
  Purchase #7 $95.34   11.795%   $106.5854   $106.59   $106.60   $106.60  
  7 purchase totals = $745.55       $823.8928   $823.90   $823.95   $823.90