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 $119.59   10.166%   $131.7475   $131.75   $131.75   $131.70  
  Purchase #2 $197.26   5.780%   $208.6616   $208.66   $208.65   $208.70  
  Purchase #3 $74.61   9.598%   $81.7711   $81.77   $81.75   $81.80  
  Purchase #4 $85.26   12.281%   $95.7308   $95.73   $95.75   $95.70  
  Purchase #5 $165.78   8.652%   $180.1233   $180.12   $180.10   $180.10  
  Purchase #6 $141.86   11.591%   $158.303   $158.30   $158.30   $158.30  
  Purchase #7 $151.67   4.466%   $158.4436   $158.44   $158.45   $158.40  
  7 purchase totals = $936.03       $1,014.7809   $1,014.77   $1,014.75   $1,014.70