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 $32.47   11.380%   $36.1651   $36.17   $36.15   $36.20  
  Purchase #2 $244.38   6.651%   $260.6337   $260.63   $260.65   $260.60  
  Purchase #3 $111.63   9.215%   $121.9167   $121.92   $121.90   $121.90  
  Purchase #4 $241.35   7.565%   $259.6081   $259.61   $259.60   $259.60  
  Purchase #5 $109.91   8.423%   $119.1677   $119.17   $119.15   $119.20  
  Purchase #6 $158.38   3.837%   $164.457   $164.46   $164.45   $164.50  
  Purchase #7 $96.94   11.797%   $108.376   $108.38   $108.40   $108.40  
  7 purchase totals = $995.06       $1,070.3243   $1,070.34   $1,070.30   $1,070.40