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 $206.44   12.644%   $232.5423   $232.54   $232.55   $232.50  
  Purchase #2 $69.99   11.730%   $78.1998   $78.20   $78.20   $78.20  
  Purchase #3 $56.32   3.318%   $58.1887   $58.19   $58.20   $58.20  
  Purchase #4 $145.68   11.765%   $162.8193   $162.82   $162.80   $162.80  
  Purchase #5 $81.77   6.304%   $86.9248   $86.92   $86.90   $86.90  
  Purchase #6 $204.40   8.568%   $221.913   $221.91   $221.90   $221.90  
  Purchase #7 $60.52   3.206%   $62.4603   $62.46   $62.45   $62.50  
  7 purchase totals = $825.12       $903.0482   $903.04   $903.00   $903.00