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 $202.98   11.710%   $226.749   $226.75   $226.75   $226.70  
  Purchase #2 $90.40   4.513%   $94.4798   $94.48   $94.50   $94.50  
  Purchase #3 $109.82   4.437%   $114.6927   $114.69   $114.70   $114.70  
  Purchase #4 $188.38   3.192%   $194.3931   $194.39   $194.40   $194.40  
  Purchase #5 $46.40   9.235%   $50.685   $50.69   $50.70   $50.70  
  Purchase #6 $96.34   11.797%   $107.7052   $107.71   $107.70   $107.70  
  Purchase #7 $198.79   10.640%   $219.9413   $219.94   $219.95   $219.90  
  7 purchase totals = $933.11       $1,008.6461   $1,008.65   $1,008.70   $1,008.60