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 $61.90   5.192%   $65.1138   $65.11   $65.10   $65.10  
  Purchase #2 $243.71   12.687%   $274.6295   $274.63   $274.65   $274.60  
  Purchase #3 $141.30   6.374%   $150.3065   $150.31   $150.30   $150.30  
  Purchase #4 $155.73   12.422%   $175.0748   $175.07   $175.05   $175.10  
  Purchase #5 $246.51   8.654%   $267.843   $267.84   $267.85   $267.80  
  Purchase #6 $113.45   5.567%   $119.7658   $119.77   $119.75   $119.80  
  Purchase #7 $206.59   8.680%   $224.522   $224.52   $224.50   $224.50  
  7 purchase totals = $1,169.19       $1,277.2554   $1,277.25   $1,277.20   $1,277.20