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	$34.73	10.118%	$38.244	$38.24	$38.25	$38.20
Purchase #2	$176.66	4.771%	$185.0884	$185.09	$185.10	$185.10
Purchase #3	$103.37	7.587%	$111.2127	$111.21	$111.20	$111.20
Purchase #4	$179.81	6.759%	$191.9634	$191.96	$191.95	$192.00
Purchase #5	$128.39	13.593%	$145.8421	$145.84	$145.85	$145.80
Purchase #6	$111.75	3.709%	$115.8948	$115.89	$115.90	$115.90
Purchase #7	$80.48	3.766%	$83.5109	$83.51	$83.50	$83.50
7 purchase totals =	$815.19		$871.7563	$871.74	$871.75	$871.70