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	$52.40	6.769%	$55.947	$55.95	$55.95	$55.90
Purchase #2	$212.98	4.302%	$222.1424	$222.14	$222.15	$222.10
Purchase #3	$217.31	12.120%	$243.648	$243.65	$243.65	$243.60
Purchase #4	$242.52	4.680%	$253.8699	$253.87	$253.85	$253.90
Purchase #5	$207.43	13.718%	$235.8852	$235.89	$235.90	$235.90
Purchase #6	$101.52	11.614%	$113.3105	$113.31	$113.30	$113.30
Purchase #7	$146.36	4.521%	$152.9769	$152.98	$153.00	$153.00
7 purchase totals =	$1,180.52		$1,277.7799	$1,277.79	$1,277.80	$1,277.70