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 $32.93   6.843%   $35.1834   $35.18   $35.20   $35.20  
  Purchase #2 $202.29   11.558%   $225.6707   $225.67   $225.65   $225.70  
  Purchase #3 $225.58   13.825%   $256.7664   $256.77   $256.75   $256.80  
  Purchase #4 $128.75   10.386%   $142.122   $142.12   $142.10   $142.10  
  Purchase #5 $119.99   11.267%   $133.5093   $133.51   $133.50   $133.50  
  Purchase #6 $244.87   4.108%   $254.9293   $254.93   $254.95   $254.90  
  Purchase #7 $69.28   5.404%   $73.0239   $73.02   $73.00   $73.00  
  7 purchase totals = $1,023.69       $1,121.2050   $1,121.20   $1,121.15   $1,121.20