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 $110.54   12.603%   $124.4714   $124.47   $124.45   $124.50  
  Purchase #2 $199.68   8.775%   $217.2019   $217.20   $217.20   $217.20  
  Purchase #3 $213.83   5.645%   $225.9007   $225.90   $225.90   $225.90  
  Purchase #4 $46.92   4.785%   $49.1651   $49.17   $49.15   $49.20  
  Purchase #5 $228.94   9.381%   $250.4169   $250.42   $250.40   $250.40  
  Purchase #6 $164.74   10.467%   $181.9833   $181.98   $182.00   $182.00  
  Purchase #7 $229.60   5.799%   $242.9145   $242.91   $242.90   $242.90  
  7 purchase totals = $1,194.25       $1,292.0538   $1,292.05   $1,292.00   $1,292.10