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 $113.76   10.873%   $126.1291   $126.13   $126.15   $126.10  
  Purchase #2 $187.49   13.535%   $212.8668   $212.87   $212.85   $212.90  
  Purchase #3 $213.30   7.570%   $229.4468   $229.45   $229.45   $229.40  
  Purchase #4 $238.26   8.272%   $257.9689   $257.97   $257.95   $258.00  
  Purchase #5 $151.86   13.219%   $171.9344   $171.93   $171.95   $171.90  
  Purchase #6 $139.62   13.858%   $158.9685   $158.97   $158.95   $159.00  
  Purchase #7 $197.97   3.689%   $205.2731   $205.27   $205.25   $205.30  
  7 purchase totals = $1,242.26       $1,362.5876   $1,362.59   $1,362.55   $1,362.60