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 $242.61   8.806%   $263.9742   $263.97   $263.95   $264.00  
  Purchase #2 $104.62   13.523%   $118.7678   $118.77   $118.75   $118.80  
  Purchase #3 $45.82   7.643%   $49.322   $49.32   $49.30   $49.30  
  Purchase #4 $126.31   9.153%   $137.8712   $137.87   $137.85   $137.90  
  Purchase #5 $91.92   13.693%   $104.5066   $104.51   $104.50   $104.50  
  Purchase #6 $248.99   6.398%   $264.9204   $264.92   $264.90   $264.90  
  Purchase #7 $130.68   13.434%   $148.2356   $148.24   $148.25   $148.20  
  7 purchase totals = $990.95       $1,087.5978   $1,087.60   $1,087.50   $1,087.60