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	$39.76	10.438%	$43.9101	$43.91	$43.90	$43.90
Purchase #2	$25.53	12.123%	$28.625	$28.63	$28.65	$28.60
Purchase #3	$218.66	7.842%	$235.8073	$235.81	$235.80	$235.80
Purchase #4	$95.83	11.521%	$106.8706	$106.87	$106.85	$106.90
Purchase #5	$21.28	5.116%	$22.3687	$22.37	$22.35	$22.40
Purchase #6	$51.59	5.268%	$54.3078	$54.31	$54.30	$54.30
Purchase #7	$25.51	11.581%	$28.4643	$28.46	$28.45	$28.50
7 purchase totals =	$478.16		$520.3538	$520.36	$520.30	$520.40