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 $66.65   13.525%   $75.6644   $75.66   $75.65   $75.70  
  Purchase #2 $217.39   12.624%   $244.8333   $244.83   $244.85   $244.80  
  Purchase #3 $104.42   9.830%   $114.6845   $114.68   $114.70   $114.70  
  Purchase #4 $94.41   3.466%   $97.6823   $97.68   $97.70   $97.70  
  Purchase #5 $242.25   5.647%   $255.9299   $255.93   $255.95   $255.90  
  Purchase #6 $19.65   6.142%   $20.8569   $20.86   $20.85   $20.90  
  Purchase #7 $198.40   10.350%   $218.9344   $218.93   $218.95   $218.90  
  7 purchase totals = $943.17       $1,028.5857   $1,028.57   $1,028.65   $1,028.60