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 $208.94   12.633%   $235.3354   $235.34   $235.35   $235.30  
  Purchase #2 $223.88   12.863%   $252.6777   $252.68   $252.70   $252.70  
  Purchase #3 $42.76   4.473%   $44.6727   $44.67   $44.65   $44.70  
  Purchase #4 $43.74   8.149%   $47.3044   $47.30   $47.30   $47.30  
  Purchase #5 $119.90   4.213%   $124.9514   $124.95   $124.95   $125.00  
  Purchase #6 $90.78   13.579%   $103.107   $103.11   $103.10   $103.10  
  Purchase #7 $162.29   10.855%   $179.9066   $179.91   $179.90   $179.90  
  7 purchase totals = $892.29       $987.9552   $987.96   $987.95   $988.00