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 $241.37   4.375%   $251.9299   $251.93   $251.95   $251.90  
  Purchase #2 $226.82   10.457%   $250.5386   $250.54   $250.55   $250.50  
  Purchase #3 $75.80   8.475%   $82.2241   $82.22   $82.20   $82.20  
  Purchase #4 $166.71   9.647%   $182.7925   $182.79   $182.80   $182.80  
  Purchase #5 $183.74   11.548%   $204.9583   $204.96   $204.95   $205.00  
  Purchase #6 $114.97   6.364%   $122.2867   $122.29   $122.30   $122.30  
  Purchase #7 $100.56   8.154%   $108.7597   $108.76   $108.75   $108.80  
  7 purchase totals = $1,109.97       $1,203.4898   $1,203.49   $1,203.50   $1,203.50