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 $113.52   11.589%   $126.6758   $126.68   $126.70   $126.70  
  Purchase #2 $225.74   12.353%   $253.6257   $253.63   $253.65   $253.60  
  Purchase #3 $18.73   8.284%   $20.2816   $20.28   $20.30   $20.30  
  Purchase #4 $165.68   13.554%   $188.1363   $188.14   $188.15   $188.10  
  Purchase #5 $149.33   5.802%   $157.9941   $157.99   $158.00   $158.00  
  Purchase #6 $93.36   4.648%   $97.6994   $97.70   $97.70   $97.70  
  Purchase #7 $212.75   11.206%   $236.5908   $236.59   $236.60   $236.60  
  7 purchase totals = $979.11       $1,081.0037   $1,081.01   $1,081.10   $1,081.00