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 $67.88   12.721%   $76.515   $76.52   $76.50   $76.50  
  Purchase #2 $218.35   11.546%   $243.5607   $243.56   $243.55   $243.60  
  Purchase #3 $65.53   4.666%   $68.5876   $68.59   $68.60   $68.60  
  Purchase #4 $15.73   6.160%   $16.699   $16.70   $16.70   $16.70  
  Purchase #5 $221.61   13.642%   $251.842   $251.84   $251.85   $251.80  
  Purchase #6 $186.65   4.595%   $195.2266   $195.23   $195.25   $195.20  
  Purchase #7 $82.62   13.779%   $94.0042   $94.00   $94.00   $94.00  
  7 purchase totals = $858.37       $946.4351   $946.44   $946.45   $946.40