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 $117.59   13.575%   $133.5528   $133.55   $133.55   $133.60  
  Purchase #2 $202.75   6.275%   $215.4726   $215.47   $215.45   $215.50  
  Purchase #3 $171.72   8.865%   $186.943   $186.94   $186.95   $186.90  
  Purchase #4 $244.44   7.690%   $263.2374   $263.24   $263.25   $263.20  
  Purchase #5 $75.73   13.463%   $85.9255   $85.93   $85.95   $85.90  
  Purchase #6 $169.50   6.247%   $180.0887   $180.09   $180.10   $180.10  
  Purchase #7 $153.72   10.718%   $170.1957   $170.20   $170.20   $170.20  
  7 purchase totals = $1,135.45       $1,235.4157   $1,235.42   $1,235.45   $1,235.40