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 $234.38   12.106%   $262.754   $262.75   $262.75   $262.80  
  Purchase #2 $121.33   13.620%   $137.8551   $137.86   $137.85   $137.90  
  Purchase #3 $230.77   13.811%   $262.6416   $262.64   $262.65   $262.60  
  Purchase #4 $236.34   12.394%   $265.632   $265.63   $265.65   $265.60  
  Purchase #5 $98.44   8.809%   $107.1116   $107.11   $107.10   $107.10  
  Purchase #6 $99.95   11.586%   $111.5302   $111.53   $111.55   $111.50  
  Purchase #7 $238.43   11.347%   $265.4847   $265.48   $265.50   $265.50  
  7 purchase totals = $1,259.64       $1,413.0092   $1,413.00   $1,413.05   $1,413.00