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	$247.79	12.759%	$279.4055	$279.41	$279.40	$279.40
Purchase #2	$85.72	6.179%	$91.0166	$91.02	$91.00	$91.00
Purchase #3	$244.68	12.213%	$274.5628	$274.56	$274.55	$274.60
Purchase #4	$33.60	12.273%	$37.7237	$37.72	$37.70	$37.70
Purchase #5	$40.41	3.392%	$41.7807	$41.78	$41.80	$41.80
Purchase #6	$19.89	4.565%	$20.798	$20.80	$20.80	$20.80
Purchase #7	$173.72	4.859%	$182.1611	$182.16	$182.15	$182.20
7 purchase totals =	$845.81		$927.4484	$927.45	$927.40	$927.50