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 $188.92   13.435%   $214.3014   $214.30   $214.30   $214.30  
  Purchase #2 $157.95   8.726%   $171.7327   $171.73   $171.75   $171.70  
  Purchase #3 $146.27   4.828%   $153.3319   $153.33   $153.35   $153.30  
  Purchase #4 $101.48   12.430%   $114.094   $114.09   $114.10   $114.10  
  Purchase #5 $223.70   4.173%   $233.035   $233.04   $233.05   $233.00  
  Purchase #6 $206.70   6.570%   $220.2802   $220.28   $220.30   $220.30  
  Purchase #7 $234.83   11.359%   $261.5043   $261.50   $261.50   $261.50  
  7 purchase totals = $1,259.85       $1,368.2795   $1,368.27   $1,368.35   $1,368.20