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	$79.25	4.126%	$82.5199	$82.52	$82.50	$82.50
Purchase #2	$71.78	11.510%	$80.0419	$80.04	$80.05	$80.00
Purchase #3	$92.53	4.674%	$96.8549	$96.85	$96.85	$96.90
Purchase #4	$95.72	6.253%	$101.7054	$101.71	$101.70	$101.70
Purchase #5	$122.39	5.316%	$128.8963	$128.90	$128.90	$128.90
Purchase #6	$59.50	13.370%	$67.4552	$67.46	$67.45	$67.50
Purchase #7	$36.74	3.532%	$38.0377	$38.04	$38.05	$38.00
7 purchase totals =	$557.91		$595.5113	$595.52	$595.50	$595.50