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	$87.56	13.743%	$99.5934	$99.59	$99.60	$99.60
Purchase #2	$168.54	3.695%	$174.7676	$174.77	$174.75	$174.80
Purchase #3	$68.60	5.502%	$72.3744	$72.37	$72.35	$72.40
Purchase #4	$150.57	11.498%	$167.8825	$167.88	$167.90	$167.90
Purchase #5	$134.60	3.322%	$139.0714	$139.07	$139.05	$139.10
Purchase #6	$190.51	13.364%	$215.9698	$215.97	$215.95	$216.00
Purchase #7	$242.82	12.798%	$273.8961	$273.90	$273.90	$273.90
7 purchase totals =	$1,043.20		$1,143.5552	$1,143.55	$1,143.50	$1,143.70