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 $224.51   13.548%   $254.9266   $254.93   $254.95   $254.90  
  Purchase #2 $50.99   7.112%   $54.6164   $54.62   $54.60   $54.60  
  Purchase #3 $202.39   5.144%   $212.8009   $212.80   $212.80   $212.80  
  Purchase #4 $179.27   10.343%   $197.8119   $197.81   $197.80   $197.80  
  Purchase #5 $113.86   4.369%   $118.8345   $118.83   $118.85   $118.80  
  Purchase #6 $236.71   5.578%   $249.9137   $249.91   $249.90   $249.90  
  Purchase #7 $30.40   12.734%   $34.2711   $34.27   $34.25   $34.30  
  7 purchase totals = $1,038.13       $1,123.1751   $1,123.17   $1,123.15   $1,123.10