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 $177.77   12.111%   $199.2997   $199.30   $199.30   $199.30  
  Purchase #2 $72.54   5.195%   $76.3085   $76.31   $76.30   $76.30  
  Purchase #3 $62.93   9.210%   $68.7259   $68.73   $68.75   $68.70  
  Purchase #4 $150.39   13.374%   $170.5032   $170.50   $170.50   $170.50  
  Purchase #5 $196.51   3.803%   $203.9833   $203.98   $204.00   $204.00  
  Purchase #6 $67.26   13.447%   $76.3045   $76.30   $76.30   $76.30  
  Purchase #7 $177.82   13.608%   $202.0177   $202.02   $202.00   $202.00  
  7 purchase totals = $905.22       $997.1428   $997.14   $997.15   $997.10