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 $59.83   3.841%   $62.1281   $62.13   $62.15   $62.10  
  Purchase #2 $182.67   3.147%   $188.4186   $188.42   $188.40   $188.40  
  Purchase #3 $202.45   13.198%   $229.1694   $229.17   $229.15   $229.20  
  Purchase #4 $138.36   5.149%   $145.4842   $145.48   $145.50   $145.50  
  Purchase #5 $208.43   10.352%   $230.0067   $230.01   $230.00   $230.00  
  Purchase #6 $113.56   11.586%   $126.7171   $126.72   $126.70   $126.70  
  Purchase #7 $29.73   7.608%   $31.9919   $31.99   $32.00   $32.00  
  7 purchase totals = $935.03       $1,013.9160   $1,013.92   $1,013.90   $1,013.90