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 $96.41   5.227%   $101.4494   $101.45   $101.45   $101.40  
  Purchase #2 $28.50   12.312%   $32.0089   $32.01   $32.00   $32.00  
  Purchase #3 $221.37   9.439%   $242.2651   $242.27   $242.25   $242.30  
  Purchase #4 $191.43   11.327%   $213.1133   $213.11   $213.10   $213.10  
  Purchase #5 $214.36   8.204%   $231.9461   $231.95   $231.95   $231.90  
  Purchase #6 $236.92   13.533%   $268.9824   $268.98   $269.00   $269.00  
  Purchase #7 $72.43   6.771%   $77.3342   $77.33   $77.35   $77.30  
  7 purchase totals = $1,061.42       $1,167.0994   $1,167.10   $1,167.10   $1,167.00