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 $131.89   12.796%   $148.7666   $148.77   $148.75   $148.80  
  Purchase #2 $54.95   11.335%   $61.1786   $61.18   $61.20   $61.20  
  Purchase #3 $125.63   12.754%   $141.6529   $141.65   $141.65   $141.70  
  Purchase #4 $47.53   13.575%   $53.9822   $53.98   $54.00   $54.00  
  Purchase #5 $250.62   4.859%   $262.7976   $262.80   $262.80   $262.80  
  Purchase #6 $130.30   10.775%   $144.3398   $144.34   $144.35   $144.30  
  Purchase #7 $221.57   3.206%   $228.6735   $228.67   $228.65   $228.70  
  7 purchase totals = $962.49       $1,041.3912   $1,041.39   $1,041.40   $1,041.50