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 $118.66   11.785%   $132.6441   $132.64   $132.65   $132.60  
  Purchase #2 $67.53   10.342%   $74.514   $74.51   $74.50   $74.50  
  Purchase #3 $109.61   8.476%   $118.9005   $118.90   $118.90   $118.90  
  Purchase #4 $64.65   3.252%   $66.7524   $66.75   $66.75   $66.80  
  Purchase #5 $72.41   11.865%   $81.0014   $81.00   $81.00   $81.00  
  Purchase #6 $175.70   10.413%   $193.9956   $194.00   $194.00   $194.00  
  Purchase #7 $125.39   11.871%   $140.275   $140.28   $140.30   $140.30  
  7 purchase totals = $733.95       $808.0830   $808.08   $808.10   $808.10