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	$25.51	13.222%	$28.8829	$28.88	$28.90	$28.90
Purchase #2	$46.92	13.581%	$53.2922	$53.29	$53.30	$53.30
Purchase #3	$155.52	8.794%	$169.1964	$169.20	$169.20	$169.20
Purchase #4	$64.96	11.337%	$72.3245	$72.32	$72.30	$72.30
Purchase #5	$144.63	3.422%	$149.5792	$149.58	$149.60	$149.60
Purchase #6	$159.76	7.668%	$172.0104	$172.01	$172.00	$172.00
Purchase #7	$238.73	13.352%	$270.6052	$270.61	$270.60	$270.60
7 purchase totals =	$836.03		$915.8908	$915.89	$915.90	$915.90