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	$162.54	7.666%	$175.0003	$175.00	$175.00	$175.00
Purchase #2	$136.88	8.813%	$148.9432	$148.94	$148.95	$148.90
Purchase #3	$162.27	10.824%	$179.8341	$179.83	$179.85	$179.80
Purchase #4	$165.81	3.767%	$172.0561	$172.06	$172.05	$172.10
Purchase #5	$48.32	12.108%	$54.1706	$54.17	$54.15	$54.20
Purchase #6	$78.69	13.249%	$89.1156	$89.12	$89.10	$89.10
Purchase #7	$148.56	8.409%	$161.0524	$161.05	$161.05	$161.10
7 purchase totals =	$903.07		$980.1723	$980.17	$980.15	$980.20