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 $144.26   4.828%   $151.2249   $151.22   $151.20   $151.20  
  Purchase #2 $125.97   12.624%   $141.8725   $141.87   $141.85   $141.90  
  Purchase #3 $232.54   13.314%   $263.5004   $263.50   $263.50   $263.50  
  Purchase #4 $148.84   5.544%   $157.0917   $157.09   $157.10   $157.10  
  Purchase #5 $15.28   9.699%   $16.762   $16.76   $16.75   $16.80  
  Purchase #6 $118.67   11.270%   $132.0441   $132.04   $132.05   $132.00  
  Purchase #7 $164.53   4.137%   $171.3366   $171.34   $171.35   $171.30  
  7 purchase totals = $950.09       $1,033.8322   $1,033.82   $1,033.80   $1,033.80