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 $23.82   11.681%   $26.6024   $26.60   $26.60   $26.60  
  Purchase #2 $180.61   9.462%   $197.6993   $197.70   $197.70   $197.70  
  Purchase #3 $132.48   12.262%   $148.7247   $148.72   $148.70   $148.70  
  Purchase #4 $167.59   7.704%   $180.5011   $180.50   $180.50   $180.50  
  Purchase #5 $169.30   5.529%   $178.6606   $178.66   $178.65   $178.70  
  Purchase #6 $44.76   6.108%   $47.4939   $47.49   $47.50   $47.50  
  Purchase #7 $34.38   7.539%   $36.9719   $36.97   $36.95   $37.00  
  7 purchase totals = $752.94       $816.6539   $816.64   $816.60   $816.70