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 $133.37   5.438%   $140.6227   $140.62   $140.60   $140.60  
  Purchase #2 $209.25   13.522%   $237.5448   $237.54   $237.55   $237.50  
  Purchase #3 $131.73   10.460%   $145.509   $145.51   $145.50   $145.50  
  Purchase #4 $129.47   8.785%   $140.8439   $140.84   $140.85   $140.80  
  Purchase #5 $91.49   9.420%   $100.1084   $100.11   $100.10   $100.10  
  Purchase #6 $27.74   7.497%   $29.8197   $29.82   $29.80   $29.80  
  Purchase #7 $44.35   7.453%   $47.6554   $47.66   $47.65   $47.70  
  7 purchase totals = $767.40       $842.1039   $842.10   $842.05   $842.00