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 $231.52   12.431%   $260.3003   $260.30   $260.30   $260.30  
  Purchase #2 $73.71   5.324%   $77.6343   $77.63   $77.65   $77.60  
  Purchase #3 $21.59   9.759%   $23.697   $23.70   $23.70   $23.70  
  Purchase #4 $224.43   10.153%   $247.2164   $247.22   $247.20   $247.20  
  Purchase #5 $200.44   3.262%   $206.9784   $206.98   $207.00   $207.00  
  Purchase #6 $174.78   9.634%   $191.6183   $191.62   $191.60   $191.60  
  Purchase #7 $144.70   11.425%   $161.232   $161.23   $161.25   $161.20  
  7 purchase totals = $1,071.17       $1,168.6767   $1,168.68   $1,168.70   $1,168.60