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 $238.98   5.229%   $251.4763   $251.48   $251.50   $251.50  
  Purchase #2 $216.47   12.673%   $243.9032   $243.90   $243.90   $243.90  
  Purchase #3 $171.99   11.580%   $191.9064   $191.91   $191.90   $191.90  
  Purchase #4 $32.49   3.860%   $33.7441   $33.74   $33.75   $33.70  
  Purchase #5 $6.79   5.492%   $7.1629   $7.16   $7.15   $7.20  
  Purchase #6 $200.49   8.700%   $217.9326   $217.93   $217.95   $217.90  
  Purchase #7 $166.56   5.797%   $176.2155   $176.22   $176.20   $176.20  
  7 purchase totals = $1,033.77       $1,122.3410   $1,122.34   $1,122.35   $1,122.30