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 $23.74   13.321%   $26.9024   $26.90   $26.90   $26.90  
  Purchase #2 $69.56   5.378%   $73.3009   $73.30   $73.30   $73.30  
  Purchase #3 $241.64   9.152%   $263.7549   $263.75   $263.75   $263.80  
  Purchase #4 $127.78   4.463%   $133.4828   $133.48   $133.50   $133.50  
  Purchase #5 $156.68   7.575%   $168.5485   $168.55   $168.55   $168.50  
  Purchase #6 $190.50   5.446%   $200.8746   $200.87   $200.85   $200.90  
  Purchase #7 $210.47   11.195%   $234.0321   $234.03   $234.05   $234.00  
  7 purchase totals = $1,020.37       $1,100.8962   $1,100.88   $1,100.90   $1,100.90