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	$27.37	8.432%	$29.6778	$29.68	$29.70	$29.70
Purchase #2	$56.27	10.482%	$62.1682	$62.17	$62.15	$62.20
Purchase #3	$216.63	12.852%	$244.4713	$244.47	$244.45	$244.50
Purchase #4	$88.64	4.809%	$92.9027	$92.90	$92.90	$92.90
Purchase #5	$79.80	13.467%	$90.5467	$90.55	$90.55	$90.50
Purchase #6	$116.91	6.349%	$124.3326	$124.33	$124.35	$124.30
Purchase #7	$54.71	8.581%	$59.4047	$59.40	$59.40	$59.40
7 purchase totals =	$640.33		$703.5040	$703.50	$703.50	$703.50