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 $88.86   8.642%   $96.5393   $96.54   $96.55   $96.50  
  Purchase #2 $71.83   10.492%   $79.3664   $79.37   $79.35   $79.40  
  Purchase #3 $45.86   13.793%   $52.1855   $52.19   $52.20   $52.20  
  Purchase #4 $17.38   5.331%   $18.3065   $18.31   $18.30   $18.30  
  Purchase #5 $25.65   7.197%   $27.496   $27.50   $27.50   $27.50  
  Purchase #6 $27.38   9.259%   $29.9151   $29.92   $29.90   $29.90  
  Purchase #7 $117.52   6.451%   $125.1012   $125.10   $125.10   $125.10  
  7 purchase totals = $394.48       $428.9100   $428.93   $428.90   $428.90