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 $178.39   8.758%   $194.0134   $194.01   $194.00   $194.00  
  Purchase #2 $36.65   5.147%   $38.5364   $38.54   $38.55   $38.50  
  Purchase #3 $60.31   4.422%   $62.9769   $62.98   $63.00   $63.00  
  Purchase #4 $57.30   9.175%   $62.5573   $62.56   $62.55   $62.60  
  Purchase #5 $99.83   6.782%   $106.6005   $106.60   $106.60   $106.60  
  Purchase #6 $243.87   8.111%   $263.6503   $263.65   $263.65   $263.70  
  Purchase #7 $58.85   12.418%   $66.158   $66.16   $66.15   $66.20  
  7 purchase totals = $735.20       $794.4928   $794.50   $794.50   $794.60