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 $227.75   8.161%   $246.3367   $246.34   $246.35   $246.30  
  Purchase #2 $235.97   7.439%   $253.5238   $253.52   $253.50   $253.50  
  Purchase #3 $174.40   9.246%   $190.525   $190.53   $190.55   $190.50  
  Purchase #4 $46.32   10.451%   $51.1609   $51.16   $51.15   $51.20  
  Purchase #5 $145.45   5.147%   $152.9363   $152.94   $152.95   $152.90  
  Purchase #6 $220.32   11.139%   $244.8614   $244.86   $244.85   $244.90  
  Purchase #7 $41.81   5.659%   $44.176   $44.18   $44.20   $44.20  
  7 purchase totals = $1,092.02       $1,183.5201   $1,183.53   $1,183.55   $1,183.50