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 $204.68   10.148%   $225.4509   $225.45   $225.45   $225.50  
  Purchase #2 $104.68   9.686%   $114.8193   $114.82   $114.80   $114.80  
  Purchase #3 $151.78   4.375%   $158.4204   $158.42   $158.40   $158.40  
  Purchase #4 $17.52   10.386%   $19.3396   $19.34   $19.35   $19.30  
  Purchase #5 $185.35   12.690%   $208.8709   $208.87   $208.85   $208.90  
  Purchase #6 $171.51   12.601%   $193.122   $193.12   $193.10   $193.10  
  Purchase #7 $59.51   12.655%   $67.041   $67.04   $67.05   $67.00  
  7 purchase totals = $895.03       $987.0641   $987.06   $987.00   $987.00