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 $186.36   11.828%   $208.4027   $208.40   $208.40   $208.40  
  Purchase #2 $59.49   9.777%   $65.3063   $65.31   $65.30   $65.30  
  Purchase #3 $117.73   13.733%   $133.8979   $133.90   $133.90   $133.90  
  Purchase #4 $237.90   10.585%   $263.0817   $263.08   $263.10   $263.10  
  Purchase #5 $63.53   11.711%   $70.97   $70.97   $70.95   $71.00  
  Purchase #6 $179.49   7.746%   $193.3933   $193.39   $193.40   $193.40  
  Purchase #7 $41.51   11.440%   $46.2587   $46.26   $46.25   $46.30  
  7 purchase totals = $886.01       $981.3106   $981.31   $981.30   $981.40