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 $153.65   8.810%   $167.1866   $167.19   $167.20   $167.20  
  Purchase #2 $103.42   5.411%   $109.0161   $109.02   $109.00   $109.00  
  Purchase #3 $231.28   5.599%   $244.2294   $244.23   $244.25   $244.20  
  Purchase #4 $209.44   9.483%   $229.3012   $229.30   $229.30   $229.30  
  Purchase #5 $164.29   12.562%   $184.9281   $184.93   $184.95   $184.90  
  Purchase #6 $143.64   12.277%   $161.2747   $161.27   $161.25   $161.30  
  Purchase #7 $81.55   13.482%   $92.5446   $92.54   $92.55   $92.50  
  7 purchase totals = $1,087.27       $1,188.4807   $1,188.48   $1,188.50   $1,188.40