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	$140.66	13.160%	$159.1709	$159.17	$159.15	$159.20
Purchase #2	$197.88	5.347%	$208.4606	$208.46	$208.45	$208.50
Purchase #3	$220.61	10.194%	$243.099	$243.10	$243.10	$243.10
Purchase #4	$238.48	7.369%	$256.0536	$256.05	$256.05	$256.10
Purchase #5	$87.56	3.776%	$90.8663	$90.87	$90.85	$90.90
Purchase #6	$245.69	11.574%	$274.1262	$274.13	$274.15	$274.10
Purchase #7	$79.45	3.613%	$82.3205	$82.32	$82.30	$82.30
7 purchase totals =	$1,210.33		$1,314.0971	$1,314.10	$1,314.05	$1,314.20