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 $217.53   13.674%   $247.2751   $247.28   $247.30   $247.30  
  Purchase #2 $29.58   12.495%   $33.276   $33.28   $33.30   $33.30  
  Purchase #3 $80.39   11.702%   $89.7972   $89.80   $89.80   $89.80  
  Purchase #4 $198.90   3.246%   $205.3563   $205.36   $205.35   $205.40  
  Purchase #5 $15.76   12.553%   $17.7384   $17.74   $17.75   $17.70  
  Purchase #6 $13.77   3.219%   $14.2133   $14.21   $14.20   $14.20  
  Purchase #7 $248.39   7.361%   $266.674   $266.67   $266.65   $266.70  
  7 purchase totals = $804.32       $874.3303   $874.34   $874.35   $874.40