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 $187.55   10.389%   $207.0346   $207.03   $207.05   $207.00  
  Purchase #2 $58.90   5.189%   $61.9563   $61.96   $61.95   $62.00  
  Purchase #3 $237.82   8.705%   $258.5222   $258.52   $258.50   $258.50  
  Purchase #4 $111.58   7.763%   $120.242   $120.24   $120.25   $120.20  
  Purchase #5 $182.86   9.123%   $199.5423   $199.54   $199.55   $199.50  
  Purchase #6 $150.48   3.345%   $155.5136   $155.51   $155.50   $155.50  
  Purchase #7 $237.47   9.793%   $260.7254   $260.73   $260.75   $260.70  
  7 purchase totals = $1,166.66       $1,263.5364   $1,263.53   $1,263.55   $1,263.40