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 $194.75   12.837%   $219.7501   $219.75   $219.75   $219.80  
  Purchase #2 $212.76   11.294%   $236.7891   $236.79   $236.80   $236.80  
  Purchase #3 $97.97   13.561%   $111.2557   $111.26   $111.25   $111.30  
  Purchase #4 $32.81   10.627%   $36.2967   $36.30   $36.30   $36.30  
  Purchase #5 $162.91   11.868%   $182.2442   $182.24   $182.25   $182.20  
  Purchase #6 $103.92   7.744%   $111.9676   $111.97   $111.95   $112.00  
  Purchase #7 $56.83   5.550%   $59.9841   $59.98   $60.00   $60.00  
  7 purchase totals = $861.95       $958.2875   $958.29   $958.30   $958.40