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 $225.39   12.464%   $253.4826   $253.48   $253.50   $253.50  
  Purchase #2 $82.66   7.390%   $88.7686   $88.77   $88.75   $88.80  
  Purchase #3 $163.88   8.862%   $178.403   $178.40   $178.40   $178.40  
  Purchase #4 $224.68   10.713%   $248.75   $248.75   $248.75   $248.80  
  Purchase #5 $62.95   5.645%   $66.5035   $66.50   $66.50   $66.50  
  Purchase #6 $189.72   4.547%   $198.3466   $198.35   $198.35   $198.30  
  Purchase #7 $48.93   4.372%   $51.0692   $51.07   $51.05   $51.10  
  7 purchase totals = $998.21       $1,085.3235   $1,085.32   $1,085.30   $1,085.40