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 $113.95   9.373%   $124.6305   $124.63   $124.65   $124.60  
  Purchase #2 $23.27   13.129%   $26.3251   $26.33   $26.35   $26.30  
  Purchase #3 $221.93   6.268%   $235.8406   $235.84   $235.85   $235.80  
  Purchase #4 $180.59   10.134%   $198.891   $198.89   $198.90   $198.90  
  Purchase #5 $122.63   3.789%   $127.2765   $127.28   $127.30   $127.30  
  Purchase #6 $124.29   3.181%   $128.2437   $128.24   $128.25   $128.20  
  Purchase #7 $192.60   13.487%   $218.576   $218.58   $218.60   $218.60  
  7 purchase totals = $979.26       $1,059.7834   $1,059.79   $1,059.90   $1,059.70