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	$137.30	10.416%	$151.6012	$151.60	$151.60	$151.60
Purchase #2	$10.54	12.600%	$11.868	$11.87	$11.85	$11.90
Purchase #3	$198.86	4.305%	$207.4209	$207.42	$207.40	$207.40
Purchase #4	$70.29	11.279%	$78.218	$78.22	$78.20	$78.20
Purchase #5	$88.25	7.527%	$94.8926	$94.89	$94.90	$94.90
Purchase #6	$38.49	11.419%	$42.8852	$42.89	$42.90	$42.90
Purchase #7	$249.30	7.772%	$268.6756	$268.68	$268.70	$268.70
7 purchase totals =	$793.03		$855.5615	$855.57	$855.55	$855.60