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	$17.52	5.414%	$18.4685	$18.47	$18.45	$18.50
Purchase #2	$240.43	3.430%	$248.6767	$248.68	$248.70	$248.70
Purchase #3	$10.70	4.192%	$11.1485	$11.15	$11.15	$11.10
Purchase #4	$85.76	12.566%	$96.5366	$96.54	$96.55	$96.50
Purchase #5	$132.34	5.316%	$139.3752	$139.38	$139.40	$139.40
Purchase #6	$148.77	9.155%	$162.3899	$162.39	$162.40	$162.40
Purchase #7	$58.75	5.713%	$62.1064	$62.11	$62.10	$62.10
7 purchase totals =	$694.27		$738.7018	$738.72	$738.75	$738.70