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 $231.36   5.558%   $244.219   $244.22   $244.20   $244.20  
  Purchase #2 $49.32   13.334%   $55.8963   $55.90   $55.90   $55.90  
  Purchase #3 $243.76   7.232%   $261.3887   $261.39   $261.40   $261.40  
  Purchase #4 $157.59   12.508%   $177.3014   $177.30   $177.30   $177.30  
  Purchase #5 $136.69   13.336%   $154.919   $154.92   $154.90   $154.90  
  Purchase #6 $184.63   13.343%   $209.2652   $209.27   $209.25   $209.30  
  Purchase #7 $118.70   11.689%   $132.5748   $132.57   $132.55   $132.60  
  7 purchase totals = $1,122.05       $1,235.5644   $1,235.57   $1,235.50   $1,235.60