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 $52.59   12.501%   $59.1643   $59.16   $59.15   $59.20  
  Purchase #2 $202.39   7.674%   $217.9214   $217.92   $217.90   $217.90  
  Purchase #3 $182.88   8.545%   $198.5071   $198.51   $198.50   $198.50  
  Purchase #4 $39.49   4.548%   $41.286   $41.29   $41.30   $41.30  
  Purchase #5 $175.81   5.183%   $184.9222   $184.92   $184.90   $184.90  
  Purchase #6 $65.58   6.128%   $69.5987   $69.60   $69.60   $69.60  
  Purchase #7 $97.48   5.431%   $102.7741   $102.77   $102.75   $102.80  
  7 purchase totals = $816.22       $874.1738   $874.17   $874.10   $874.20