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	$143.96	5.657%	$152.1038	$152.10	$152.10	$152.10
Purchase #2	$91.26	9.821%	$100.2226	$100.22	$100.20	$100.20
Purchase #3	$233.90	3.730%	$242.6245	$242.62	$242.60	$242.60
Purchase #4	$145.31	12.259%	$163.1236	$163.12	$163.10	$163.10
Purchase #5	$82.51	4.709%	$86.3954	$86.40	$86.40	$86.40
Purchase #6	$146.33	13.379%	$165.9075	$165.91	$165.90	$165.90
Purchase #7	$222.66	12.533%	$250.566	$250.57	$250.55	$250.60
7 purchase totals =	$1,065.93		$1,160.9434	$1,160.94	$1,160.85	$1,160.90