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 $60.84   10.519%   $67.2398   $67.24   $67.25   $67.20  
  Purchase #2 $16.86   4.720%   $17.6558   $17.66   $17.65   $17.70  
  Purchase #3 $156.90   10.446%   $173.2898   $173.29   $173.30   $173.30  
  Purchase #4 $232.39   10.859%   $257.6252   $257.63   $257.65   $257.60  
  Purchase #5 $14.94   5.691%   $15.7902   $15.79   $15.80   $15.80  
  Purchase #6 $42.42   12.211%   $47.5999   $47.60   $47.60   $47.60  
  Purchase #7 $187.33   7.807%   $201.9549   $201.95   $201.95   $202.00  
  7 purchase totals = $711.68       $781.1556   $781.16   $781.20   $781.20