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 $226.57   10.116%   $249.4898   $249.49   $249.50   $249.50  
  Purchase #2 $172.86   12.853%   $195.0777   $195.08   $195.10   $195.10  
  Purchase #3 $5.69   5.152%   $5.9831   $5.98   $6.00   $6.00  
  Purchase #4 $226.82   11.266%   $252.3735   $252.37   $252.35   $252.40  
  Purchase #5 $69.69   9.551%   $76.3461   $76.35   $76.35   $76.30  
  Purchase #6 $141.30   11.341%   $157.3248   $157.32   $157.30   $157.30  
  Purchase #7 $243.33   6.327%   $258.7255   $258.73   $258.75   $258.70  
  7 purchase totals = $1,086.26       $1,195.3205   $1,195.32   $1,195.35   $1,195.30