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	$245.74	4.222%	$256.1151	$256.12	$256.10	$256.10
Purchase #2	$145.31	3.770%	$150.7882	$150.79	$150.80	$150.80
Purchase #3	$244.90	9.780%	$268.8512	$268.85	$268.85	$268.90
Purchase #4	$57.42	5.483%	$60.5683	$60.57	$60.55	$60.60
Purchase #5	$46.48	11.265%	$51.716	$51.72	$51.70	$51.70
Purchase #6	$225.69	5.682%	$238.5137	$238.51	$238.50	$238.50
Purchase #7	$166.94	3.259%	$172.3806	$172.38	$172.40	$172.40
7 purchase totals =	$1,132.48		$1,198.9331	$1,198.94	$1,198.90	$1,199.00