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 $75.62   10.169%   $83.3098   $83.31   $83.30   $83.30  
  Purchase #2 $250.84   13.672%   $285.1348   $285.13   $285.15   $285.10  
  Purchase #3 $39.66   7.386%   $42.5893   $42.59   $42.60   $42.60  
  Purchase #4 $111.40   4.263%   $116.149   $116.15   $116.15   $116.10  
  Purchase #5 $57.54   11.236%   $64.0052   $64.01   $64.00   $64.00  
  Purchase #6 $182.41   8.272%   $197.499   $197.50   $197.50   $197.50  
  Purchase #7 $94.46   12.559%   $106.3232   $106.32   $106.30   $106.30  
  7 purchase totals = $811.93       $895.0103   $895.01   $895.00   $894.90