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 $93.27   6.212%   $99.0639   $99.06   $99.05   $99.10  
  Purchase #2 $246.61   5.537%   $260.2648   $260.26   $260.25   $260.30  
  Purchase #3 $13.60   6.717%   $14.5135   $14.51   $14.50   $14.50  
  Purchase #4 $246.54   11.652%   $275.2668   $275.27   $275.25   $275.30  
  Purchase #5 $215.53   4.148%   $224.4702   $224.47   $224.45   $224.50  
  Purchase #6 $91.66   10.549%   $101.3292   $101.33   $101.35   $101.30  
  Purchase #7 $8.35   13.805%   $9.5027   $9.50   $9.50   $9.50  
  7 purchase totals = $915.56       $984.4111   $984.40   $984.35   $984.50