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 $46.69   8.432%   $50.6269   $50.63   $50.65   $50.60  
  Purchase #2 $125.88   13.276%   $142.5918   $142.59   $142.60   $142.60  
  Purchase #3 $222.26   12.140%   $249.2424   $249.24   $249.25   $249.20  
  Purchase #4 $216.90   10.349%   $239.347   $239.35   $239.35   $239.30  
  Purchase #5 $119.74   4.361%   $124.9619   $124.96   $124.95   $125.00  
  Purchase #6 $56.62   3.381%   $58.5343   $58.53   $58.55   $58.50  
  Purchase #7 $202.47   9.624%   $221.9557   $221.96   $221.95   $222.00  
  7 purchase totals = $990.56       $1,087.2600   $1,087.26   $1,087.30   $1,087.20