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 $233.67   12.659%   $263.2503   $263.25   $263.25   $263.30  
  Purchase #2 $190.84   3.779%   $198.0518   $198.05   $198.05   $198.10  
  Purchase #3 $169.79   4.163%   $176.8584   $176.86   $176.85   $176.90  
  Purchase #4 $127.66   5.761%   $135.0145   $135.01   $135.00   $135.00  
  Purchase #5 $218.61   3.222%   $225.6536   $225.65   $225.65   $225.70  
  Purchase #6 $214.83   9.213%   $234.6223   $234.62   $234.60   $234.60  
  Purchase #7 $239.50   6.814%   $255.8195   $255.82   $255.80   $255.80  
  7 purchase totals = $1,394.90       $1,489.2704   $1,489.26   $1,489.20   $1,489.40