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	$199.88	4.771%	$209.4163	$209.42	$209.40	$209.40
Purchase #2	$202.82	6.782%	$216.5753	$216.58	$216.60	$216.60
Purchase #3	$142.46	10.299%	$157.132	$157.13	$157.15	$157.10
Purchase #4	$144.50	10.612%	$159.8343	$159.83	$159.85	$159.80
Purchase #5	$106.83	11.829%	$119.4669	$119.47	$119.45	$119.50
Purchase #6	$145.82	4.647%	$152.5963	$152.60	$152.60	$152.60
Purchase #7	$211.26	12.130%	$236.8858	$236.89	$236.90	$236.90
7 purchase totals =	$1,153.57		$1,251.9069	$1,251.92	$1,251.95	$1,251.90