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 $12.38   3.642%   $12.8309   $12.83   $12.85   $12.80  
  Purchase #2 $8.98   8.437%   $9.7376   $9.74   $9.75   $9.70  
  Purchase #3 $47.44   8.492%   $51.4686   $51.47   $51.45   $51.50  
  Purchase #4 $7.77   5.353%   $8.1859   $8.19   $8.20   $8.20  
  Purchase #5 $191.60   4.775%   $200.7489   $200.75   $200.75   $200.70  
  Purchase #6 $119.25   7.386%   $128.0578   $128.06   $128.05   $128.10  
  Purchase #7 $140.59   9.303%   $153.6691   $153.67   $153.65   $153.70  
  7 purchase totals = $528.01       $564.6988   $564.71   $564.70   $564.70