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	$28.35	6.224%	$30.1145	$30.11	$30.10	$30.10
Purchase #2	$159.42	6.152%	$169.2275	$169.23	$169.25	$169.20
Purchase #3	$209.80	5.399%	$221.1271	$221.13	$221.15	$221.10
Purchase #4	$250.97	3.116%	$258.7902	$258.79	$258.80	$258.80
Purchase #5	$212.46	13.383%	$240.8935	$240.89	$240.90	$240.90
Purchase #6	$74.88	5.198%	$78.7723	$78.77	$78.75	$78.80
Purchase #7	$153.38	12.500%	$172.5525	$172.55	$172.55	$172.60
7 purchase totals =	$1,089.26		$1,171.4776	$1,171.47	$1,171.50	$1,171.50