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 $206.69   11.166%   $229.769   $229.77   $229.75   $229.80  
  Purchase #2 $204.34   3.634%   $211.7657   $211.77   $211.75   $211.80  
  Purchase #3 $156.93   10.568%   $173.5144   $173.51   $173.50   $173.50  
  Purchase #4 $229.57   11.663%   $256.3447   $256.34   $256.35   $256.30  
  Purchase #5 $96.33   5.763%   $101.8815   $101.88   $101.90   $101.90  
  Purchase #6 $103.92   8.679%   $112.9392   $112.94   $112.95   $112.90  
  Purchase #7 $6.36   9.703%   $6.9771   $6.98   $7.00   $7.00  
  7 purchase totals = $1,004.14       $1,093.1916   $1,093.19   $1,093.20   $1,093.20