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 $187.57   7.717%   $202.0448   $202.04   $202.05   $202.00  
  Purchase #2 $30.94   13.191%   $35.0213   $35.02   $35.00   $35.00  
  Purchase #3 $153.34   8.466%   $166.3218   $166.32   $166.30   $166.30  
  Purchase #4 $240.59   6.472%   $256.161   $256.16   $256.15   $256.20  
  Purchase #5 $49.64   4.582%   $51.9145   $51.91   $51.90   $51.90  
  Purchase #6 $203.71   5.748%   $215.4193   $215.42   $215.40   $215.40  
  Purchase #7 $246.69   12.843%   $278.3724   $278.37   $278.35   $278.40  
  7 purchase totals = $1,112.48       $1,205.2551   $1,205.24   $1,205.15   $1,205.20