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 $216.82   4.201%   $225.9286   $225.93   $225.95   $225.90  
  Purchase #2 $110.98   13.518%   $125.9823   $125.98   $126.00   $126.00  
  Purchase #3 $56.37   11.188%   $62.6767   $62.68   $62.70   $62.70  
  Purchase #4 $108.44   3.734%   $112.4891   $112.49   $112.50   $112.50  
  Purchase #5 $101.29   6.422%   $107.7948   $107.79   $107.80   $107.80  
  Purchase #6 $60.32   3.790%   $62.6061   $62.61   $62.60   $62.60  
  Purchase #7 $232.30   4.132%   $241.8986   $241.90   $241.90   $241.90  
  7 purchase totals = $886.52       $939.3762   $939.38   $939.45   $939.40