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 $118.93   11.243%   $132.3013   $132.30   $132.30   $132.30  
  Purchase #2 $156.37   3.165%   $161.3191   $161.32   $161.30   $161.30  
  Purchase #3 $187.92   10.464%   $207.5839   $207.58   $207.60   $207.60  
  Purchase #4 $50.34   8.826%   $54.783   $54.78   $54.80   $54.80  
  Purchase #5 $153.50   13.738%   $174.5878   $174.59   $174.60   $174.60  
  Purchase #6 $102.89   5.433%   $108.48   $108.48   $108.50   $108.50  
  Purchase #7 $41.59   11.598%   $46.4136   $46.41   $46.40   $46.40  
  7 purchase totals = $811.54       $885.4687   $885.46   $885.50   $885.50