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 $69.78   4.823%   $73.1455   $73.15   $73.15   $73.10  
  Purchase #2 $230.73   9.103%   $251.7334   $251.73   $251.75   $251.70  
  Purchase #3 $228.42   6.122%   $242.4039   $242.40   $242.40   $242.40  
  Purchase #4 $185.35   11.253%   $206.2074   $206.21   $206.20   $206.20  
  Purchase #5 $57.42   8.493%   $62.2967   $62.30   $62.30   $62.30  
  Purchase #6 $96.62   6.516%   $102.9158   $102.92   $102.90   $102.90  
  Purchase #7 $88.48   9.216%   $96.6343   $96.63   $96.65   $96.60  
  7 purchase totals = $956.80       $1,035.3370   $1,035.34   $1,035.35   $1,035.20