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	$144.39	10.477%	$159.5177	$159.52	$159.50	$159.50
Purchase #2	$104.59	12.570%	$117.737	$117.74	$117.75	$117.70
Purchase #3	$201.73	13.263%	$228.4854	$228.49	$228.50	$228.50
Purchase #4	$160.88	7.376%	$172.7465	$172.75	$172.75	$172.70
Purchase #5	$87.36	3.290%	$90.2341	$90.23	$90.25	$90.20
Purchase #6	$230.57	5.216%	$242.5965	$242.60	$242.60	$242.60
Purchase #7	$85.26	5.314%	$89.7907	$89.79	$89.80	$89.80
7 purchase totals =	$1,014.78		$1,101.1079	$1,101.12	$1,101.15	$1,101.00