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 $67.91   8.573%   $73.7319   $73.73   $73.75   $73.70  
  Purchase #2 $112.60   5.341%   $118.614   $118.61   $118.60   $118.60  
  Purchase #3 $125.46   6.304%   $133.369   $133.37   $133.35   $133.40  
  Purchase #4 $209.56   5.704%   $221.5133   $221.51   $221.50   $221.50  
  Purchase #5 $185.73   7.476%   $199.6152   $199.62   $199.60   $199.60  
  Purchase #6 $129.48   3.192%   $133.613   $133.61   $133.60   $133.60  
  Purchase #7 $225.37   7.163%   $241.5133   $241.51   $241.50   $241.50  
  7 purchase totals = $1,056.11       $1,121.9697   $1,121.96   $1,121.90   $1,121.90