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 $14.77   6.712%   $15.7614   $15.76   $15.75   $15.80  
  Purchase #2 $127.68   4.275%   $133.1383   $133.14   $133.15   $133.10  
  Purchase #3 $147.32   5.255%   $155.0617   $155.06   $155.05   $155.10  
  Purchase #4 $248.64   13.318%   $281.7539   $281.75   $281.75   $281.80  
  Purchase #5 $57.82   13.710%   $65.7471   $65.75   $65.75   $65.70  
  Purchase #6 $69.64   9.802%   $76.4661   $76.47   $76.45   $76.50  
  Purchase #7 $215.73   3.385%   $223.0325   $223.03   $223.05   $223.00  
  7 purchase totals = $881.60       $950.9610   $950.96   $950.95   $951.00