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 $57.67   6.379%   $61.3488   $61.35   $61.35   $61.30  
  Purchase #2 $97.53   8.539%   $105.8581   $105.86   $105.85   $105.90  
  Purchase #3 $204.59   5.623%   $216.0941   $216.09   $216.10   $216.10  
  Purchase #4 $22.45   11.584%   $25.0506   $25.05   $25.05   $25.10  
  Purchase #5 $57.82   7.182%   $61.9726   $61.97   $61.95   $62.00  
  Purchase #6 $214.91   13.708%   $244.3699   $244.37   $244.35   $244.40  
  Purchase #7 $103.68   11.606%   $115.7131   $115.71   $115.70   $115.70  
  7 purchase totals = $758.65       $830.4072   $830.40   $830.35   $830.50