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 $218.58   11.146%   $242.9429   $242.94   $242.95   $242.90  
  Purchase #2 $208.35   6.213%   $221.2948   $221.29   $221.30   $221.30  
  Purchase #3 $52.27   11.616%   $58.3417   $58.34   $58.35   $58.30  
  Purchase #4 $164.34   3.578%   $170.2201   $170.22   $170.20   $170.20  
  Purchase #5 $32.96   4.617%   $34.4818   $34.48   $34.50   $34.50  
  Purchase #6 $174.43   12.230%   $195.7628   $195.76   $195.75   $195.80  
  Purchase #7 $215.77   6.193%   $229.1326   $229.13   $229.15   $229.10  
  7 purchase totals = $1,066.70       $1,152.1767   $1,152.16   $1,152.20   $1,152.10