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 $46.95   6.407%   $49.9581   $49.96   $49.95   $50.00  
  Purchase #2 $167.96   10.140%   $184.9911   $184.99   $185.00   $185.00  
  Purchase #3 $83.34   11.376%   $92.8208   $92.82   $92.80   $92.80  
  Purchase #4 $246.81   3.479%   $255.3965   $255.40   $255.40   $255.40  
  Purchase #5 $29.82   3.755%   $30.9397   $30.94   $30.95   $30.90  
  Purchase #6 $151.85   10.845%   $168.3181   $168.32   $168.30   $168.30  
  Purchase #7 $60.75   10.194%   $66.9429   $66.94   $66.95   $66.90  
  7 purchase totals = $787.48       $849.3672   $849.37   $849.35   $849.30