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 $125.35   6.290%   $133.2345   $133.23   $133.25   $133.20  
  Purchase #2 $240.29   11.311%   $267.4692   $267.47   $267.45   $267.50  
  Purchase #3 $11.78   6.750%   $12.5752   $12.58   $12.60   $12.60  
  Purchase #4 $244.69   5.720%   $258.6863   $258.69   $258.70   $258.70  
  Purchase #5 $51.58   13.396%   $58.4897   $58.49   $58.50   $58.50  
  Purchase #6 $171.67   12.681%   $193.4395   $193.44   $193.45   $193.40  
  Purchase #7 $87.87   13.541%   $99.7685   $99.77   $99.75   $99.80  
  7 purchase totals = $933.23       $1,023.6629   $1,023.67   $1,023.70   $1,023.70