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 $192.95   12.772%   $217.5936   $217.59   $217.60   $217.60  
  Purchase #2 $213.42   6.477%   $227.2432   $227.24   $227.25   $227.20  
  Purchase #3 $77.59   5.307%   $81.7077   $81.71   $81.70   $81.70  
  Purchase #4 $104.31   12.368%   $117.2111   $117.21   $117.20   $117.20  
  Purchase #5 $205.52   4.283%   $214.3224   $214.32   $214.30   $214.30  
  Purchase #6 $232.87   7.497%   $250.3283   $250.33   $250.35   $250.30  
  Purchase #7 $143.96   11.806%   $160.9559   $160.96   $160.95   $161.00  
  7 purchase totals = $1,170.62       $1,269.3622   $1,269.36   $1,269.35   $1,269.30