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 $149.44   13.467%   $169.5651   $169.57   $169.55   $169.60  
  Purchase #2 $130.83   4.183%   $136.3026   $136.30   $136.30   $136.30  
  Purchase #3 $132.34   7.530%   $142.3052   $142.31   $142.30   $142.30  
  Purchase #4 $164.42   3.809%   $170.6828   $170.68   $170.70   $170.70  
  Purchase #5 $126.51   8.805%   $137.6492   $137.65   $137.65   $137.60  
  Purchase #6 $233.80   13.870%   $266.2281   $266.23   $266.25   $266.20  
  Purchase #7 $55.90   12.185%   $62.7114   $62.71   $62.70   $62.70  
  7 purchase totals = $993.24       $1,085.4444   $1,085.45   $1,085.45   $1,085.40