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 $125.96   5.715%   $133.1586   $133.16   $133.15   $133.20  
  Purchase #2 $163.46   5.578%   $172.5778   $172.58   $172.60   $172.60  
  Purchase #3 $250.90   5.494%   $264.6844   $264.68   $264.70   $264.70  
  Purchase #4 $184.57   6.762%   $197.0506   $197.05   $197.05   $197.10  
  Purchase #5 $234.88   10.247%   $258.9482   $258.95   $258.95   $258.90  
  Purchase #6 $137.29   11.752%   $153.4243   $153.42   $153.40   $153.40  
  Purchase #7 $49.66   11.299%   $55.2711   $55.27   $55.25   $55.30  
  7 purchase totals = $1,146.72       $1,235.1150   $1,235.11   $1,235.10   $1,235.20