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	$80.49	12.832%	$90.8185	$90.82	$90.80	$90.80
Purchase #2	$116.50	13.213%	$131.8931	$131.89	$131.90	$131.90
Purchase #3	$18.56	13.495%	$21.0647	$21.06	$21.05	$21.10
Purchase #4	$229.89	7.662%	$247.5042	$247.50	$247.50	$247.50
Purchase #5	$238.52	13.710%	$271.2211	$271.22	$271.20	$271.20
Purchase #6	$241.43	12.647%	$271.9637	$271.96	$271.95	$272.00
Purchase #7	$55.95	4.585%	$58.5153	$58.52	$58.50	$58.50
7 purchase totals =	$981.34		$1,092.9806	$1,092.97	$1,092.90	$1,093.00