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 $244.98   11.173%   $272.3516   $272.35   $272.35   $272.40  
  Purchase #2 $227.82   8.623%   $247.4649   $247.46   $247.45   $247.50  
  Purchase #3 $164.26   4.435%   $171.5449   $171.54   $171.55   $171.50  
  Purchase #4 $157.98   6.398%   $168.0876   $168.09   $168.10   $168.10  
  Purchase #5 $247.43   9.542%   $271.0398   $271.04   $271.05   $271.00  
  Purchase #6 $150.53   5.616%   $158.9838   $158.98   $159.00   $159.00  
  Purchase #7 $242.78   11.171%   $269.901   $269.90   $269.90   $269.90  
  7 purchase totals = $1,435.78       $1,559.3736   $1,559.36   $1,559.40   $1,559.40