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 $165.79   6.576%   $176.6924   $176.69   $176.70   $176.70  
  Purchase #2 $85.93   7.352%   $92.2476   $92.25   $92.25   $92.20  
  Purchase #3 $161.92   6.844%   $173.0018   $173.00   $173.00   $173.00  
  Purchase #4 $157.27   3.575%   $162.8924   $162.89   $162.90   $162.90  
  Purchase #5 $83.34   9.651%   $91.3831   $91.38   $91.40   $91.40  
  Purchase #6 $88.26   7.327%   $94.7268   $94.73   $94.75   $94.70  
  Purchase #7 $72.64   4.200%   $75.6909   $75.69   $75.70   $75.70  
  7 purchase totals = $815.15       $866.6350   $866.63   $866.70   $866.60