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 $87.61   6.858%   $93.6183   $93.62   $93.60   $93.60  
  Purchase #2 $115.38   11.177%   $128.276   $128.28   $128.30   $128.30  
  Purchase #3 $183.37   3.495%   $189.7788   $189.78   $189.80   $189.80  
  Purchase #4 $72.79   4.198%   $75.8457   $75.85   $75.85   $75.80  
  Purchase #5 $199.48   3.419%   $206.3002   $206.30   $206.30   $206.30  
  Purchase #6 $234.44   9.191%   $255.9874   $255.99   $256.00   $256.00  
  Purchase #7 $74.87   11.518%   $83.4935   $83.49   $83.50   $83.50  
  7 purchase totals = $967.94       $1,033.2999   $1,033.31   $1,033.35   $1,033.30