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	$29.86	6.594%	$31.829	$31.83	$31.85	$31.80
Purchase #2	$174.37	6.133%	$185.0641	$185.06	$185.05	$185.10
Purchase #3	$59.83	7.660%	$64.413	$64.41	$64.40	$64.40
Purchase #4	$55.74	6.239%	$59.2176	$59.22	$59.20	$59.20
Purchase #5	$76.54	3.614%	$79.3062	$79.31	$79.30	$79.30
Purchase #6	$121.88	13.827%	$138.7323	$138.73	$138.75	$138.70
Purchase #7	$18.30	4.439%	$19.1123	$19.11	$19.10	$19.10
7 purchase totals =	$536.52		$577.6745	$577.67	$577.65	$577.60