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 $59.47   12.721%   $67.0352   $67.04   $67.05   $67.00  
  Purchase #2 $167.37   5.851%   $177.1628   $177.16   $177.15   $177.20  
  Purchase #3 $202.30   12.161%   $226.9017   $226.90   $226.90   $226.90  
  Purchase #4 $92.47   6.865%   $98.8181   $98.82   $98.80   $98.80  
  Purchase #5 $246.74   13.428%   $279.8722   $279.87   $279.85   $279.90  
  Purchase #6 $199.54   5.298%   $210.1116   $210.11   $210.10   $210.10  
  Purchase #7 $249.41   12.840%   $281.4342   $281.43   $281.45   $281.40  
  7 purchase totals = $1,217.30       $1,341.3358   $1,341.33   $1,341.30   $1,341.30