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 $84.67   4.567%   $88.5369   $88.54   $88.55   $88.50  
  Purchase #2 $188.26   4.706%   $197.1195   $197.12   $197.10   $197.10  
  Purchase #3 $50.39   13.431%   $57.1579   $57.16   $57.15   $57.20  
  Purchase #4 $196.41   4.581%   $205.4075   $205.41   $205.40   $205.40  
  Purchase #5 $89.85   5.596%   $94.878   $94.88   $94.90   $94.90  
  Purchase #6 $124.71   7.180%   $133.6642   $133.66   $133.65   $133.70  
  Purchase #7 $176.65   12.745%   $199.164   $199.16   $199.15   $199.20  
  7 purchase totals = $910.94       $975.9280   $975.93   $975.90   $976.00