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	$69.88	12.751%	$78.7904	$78.79	$78.80	$78.80
Purchase #2	$132.69	10.454%	$146.5614	$146.56	$146.55	$146.60
Purchase #3	$249.55	11.625%	$278.5602	$278.56	$278.55	$278.60
Purchase #4	$235.84	13.308%	$267.2256	$267.23	$267.25	$267.20
Purchase #5	$100.88	4.538%	$105.4579	$105.46	$105.45	$105.50
Purchase #6	$136.88	7.670%	$147.3787	$147.38	$147.40	$147.40
Purchase #7	$201.92	8.815%	$219.7192	$219.72	$219.70	$219.70
7 purchase totals =	$1,127.64		$1,243.6934	$1,243.70	$1,243.70	$1,243.80