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	$80.37	4.278%	$83.8082	$83.81	$83.80	$83.80
Purchase #2	$40.55	12.183%	$45.4902	$45.49	$45.50	$45.50
Purchase #3	$240.64	9.720%	$264.0302	$264.03	$264.05	$264.00
Purchase #4	$207.85	13.314%	$235.5231	$235.52	$235.50	$235.50
Purchase #5	$50.68	13.454%	$57.4985	$57.50	$57.50	$57.50
Purchase #6	$168.32	13.462%	$190.9792	$190.98	$191.00	$191.00
Purchase #7	$146.36	13.135%	$165.5844	$165.58	$165.60	$165.60
7 purchase totals =	$934.77		$1,042.9138	$1,042.91	$1,042.95	$1,042.90