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 $24.98   4.283%   $26.0499   $26.05   $26.05   $26.00  
  Purchase #2 $125.92   11.650%   $140.5897   $140.59   $140.60   $140.60  
  Purchase #3 $30.56   7.774%   $32.9357   $32.94   $32.95   $32.90  
  Purchase #4 $63.30   13.454%   $71.8164   $71.82   $71.80   $71.80  
  Purchase #5 $43.77   10.332%   $48.2923   $48.29   $48.30   $48.30  
  Purchase #6 $16.83   6.446%   $17.9149   $17.91   $17.90   $17.90  
  Purchase #7 $16.62   4.475%   $17.3637   $17.36   $17.35   $17.40  
  7 purchase totals = $321.98       $354.9626   $354.96   $354.95   $354.90