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 $249.66   6.228%   $265.2088   $265.21   $265.20   $265.20  
  Purchase #2 $121.53   8.196%   $131.4906   $131.49   $131.50   $131.50  
  Purchase #3 $83.27   4.104%   $86.6874   $86.69   $86.70   $86.70  
  Purchase #4 $58.61   6.650%   $62.5076   $62.51   $62.50   $62.50  
  Purchase #5 $53.99   13.676%   $61.3737   $61.37   $61.35   $61.40  
  Purchase #6 $43.96   9.151%   $47.9828   $47.98   $48.00   $48.00  
  Purchase #7 $203.91   11.125%   $226.595   $226.60   $226.60   $226.60  
  7 purchase totals = $814.93       $881.8459   $881.85   $881.85   $881.90