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 $69.73   12.464%   $78.4211   $78.42   $78.40   $78.40  
  Purchase #2 $103.41   8.643%   $112.3477   $112.35   $112.35   $112.30  
  Purchase #3 $224.73   9.782%   $246.7131   $246.71   $246.70   $246.70  
  Purchase #4 $199.92   3.827%   $207.5709   $207.57   $207.55   $207.60  
  Purchase #5 $144.98   6.662%   $154.6386   $154.64   $154.65   $154.60  
  Purchase #6 $158.47   6.252%   $168.3775   $168.38   $168.40   $168.40  
  Purchase #7 $211.70   12.355%   $237.8555   $237.86   $237.85   $237.90  
  7 purchase totals = $1,112.94       $1,205.9244   $1,205.93   $1,205.90   $1,205.90