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 $181.89   12.444%   $204.5244   $204.52   $204.50   $204.50  
  Purchase #2 $25.76   8.502%   $27.9501   $27.95   $27.95   $28.00  
  Purchase #3 $103.92   5.749%   $109.8944   $109.89   $109.90   $109.90  
  Purchase #4 $158.29   3.523%   $163.8666   $163.87   $163.85   $163.90  
  Purchase #5 $221.29   5.388%   $233.2131   $233.21   $233.20   $233.20  
  Purchase #6 $229.98   13.492%   $261.0089   $261.01   $261.00   $261.00  
  Purchase #7 $206.49   7.652%   $222.2906   $222.29   $222.30   $222.30  
  7 purchase totals = $1,127.62       $1,222.7481   $1,222.74   $1,222.70   $1,222.80