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 $60.54   13.276%   $68.5773   $68.58   $68.60   $68.60  
  Purchase #2 $167.84   9.538%   $183.8486   $183.85   $183.85   $183.80  
  Purchase #3 $159.53   11.420%   $177.7483   $177.75   $177.75   $177.70  
  Purchase #4 $102.84   6.162%   $109.177   $109.18   $109.20   $109.20  
  Purchase #5 $104.34   12.367%   $117.2437   $117.24   $117.25   $117.20  
  Purchase #6 $71.94   12.450%   $80.8965   $80.90   $80.90   $80.90  
  Purchase #7 $164.63   4.617%   $172.231   $172.23   $172.25   $172.20  
  7 purchase totals = $831.66       $909.7224   $909.73   $909.80   $909.60