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 $219.56   13.230%   $248.6078   $248.61   $248.60   $248.60  
  Purchase #2 $90.92   7.189%   $97.4562   $97.46   $97.45   $97.50  
  Purchase #3 $55.62   3.427%   $57.5261   $57.53   $57.55   $57.50  
  Purchase #4 $181.55   12.354%   $203.9787   $203.98   $204.00   $204.00  
  Purchase #5 $107.50   6.499%   $114.4864   $114.49   $114.50   $114.50  
  Purchase #6 $114.68   10.367%   $126.5689   $126.57   $126.55   $126.60  
  Purchase #7 $36.64   7.184%   $39.2722   $39.27   $39.25   $39.30  
  7 purchase totals = $806.47       $887.8963   $887.91   $887.90   $888.00