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 $54.77   5.184%   $57.6093   $57.61   $57.60   $57.60  
  Purchase #2 $200.30   13.506%   $227.3525   $227.35   $227.35   $227.40  
  Purchase #3 $22.31   11.329%   $24.8375   $24.84   $24.85   $24.80  
  Purchase #4 $185.59   4.656%   $194.2311   $194.23   $194.25   $194.20  
  Purchase #5 $155.42   8.616%   $168.811   $168.81   $168.80   $168.80  
  Purchase #6 $154.95   10.103%   $170.6046   $170.60   $170.60   $170.60  
  Purchase #7 $186.63   5.667%   $197.2063   $197.21   $197.20   $197.20  
  7 purchase totals = $959.97       $1,040.6523   $1,040.65   $1,040.65   $1,040.60