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	$19.89	5.172%	$20.9187	$20.92	$20.90	$20.90
Purchase #2	$46.81	7.445%	$50.295	$50.30	$50.30	$50.30
Purchase #3	$127.72	13.202%	$144.5816	$144.58	$144.60	$144.60
Purchase #4	$99.54	11.791%	$111.2768	$111.28	$111.30	$111.30
Purchase #5	$172.78	9.828%	$189.7608	$189.76	$189.75	$189.80
Purchase #6	$73.95	8.310%	$80.0952	$80.10	$80.10	$80.10
Purchase #7	$179.66	13.187%	$203.3518	$203.35	$203.35	$203.40
7 purchase totals =	$720.35		$800.2799	$800.29	$800.30	$800.40