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 $114.93   3.574%   $119.0376   $119.04   $119.05   $119.00  
  Purchase #2 $180.88   8.107%   $195.5439   $195.54   $195.55   $195.50  
  Purchase #3 $86.55   11.471%   $96.4782   $96.48   $96.50   $96.50  
  Purchase #4 $172.36   10.219%   $189.9735   $189.97   $189.95   $190.00  
  Purchase #5 $9.81   12.215%   $11.0083   $11.01   $11.00   $11.00  
  Purchase #6 $206.96   11.291%   $230.3279   $230.33   $230.35   $230.30  
  Purchase #7 $176.75   4.758%   $185.1598   $185.16   $185.15   $185.20  
  7 purchase totals = $948.24       $1,027.5292   $1,027.53   $1,027.55   $1,027.50