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 $247.87   13.411%   $281.1118   $281.11   $281.10   $281.10  
  Purchase #2 $179.96   3.308%   $185.9131   $185.91   $185.90   $185.90  
  Purchase #3 $35.55   11.515%   $39.6436   $39.64   $39.65   $39.60  
  Purchase #4 $194.68   5.559%   $205.5023   $205.50   $205.50   $205.50  
  Purchase #5 $126.42   4.565%   $132.1911   $132.19   $132.20   $132.20  
  Purchase #6 $38.60   12.853%   $43.5613   $43.56   $43.55   $43.60  
  Purchase #7 $242.50   13.304%   $274.7622   $274.76   $274.75   $274.80  
  7 purchase totals = $1,065.58       $1,162.6854   $1,162.67   $1,162.65   $1,162.70