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	$94.32	6.307%	$100.2688	$100.27	$100.25	$100.30
Purchase #2	$64.60	11.290%	$71.8933	$71.89	$71.90	$71.90
Purchase #3	$73.29	13.556%	$83.2252	$83.23	$83.25	$83.20
Purchase #4	$66.26	7.473%	$71.2116	$71.21	$71.20	$71.20
Purchase #5	$207.78	3.344%	$214.7282	$214.73	$214.75	$214.70
Purchase #6	$209.93	13.261%	$237.7688	$237.77	$237.75	$237.80
Purchase #7	$72.40	9.196%	$79.0579	$79.06	$79.05	$79.10
7 purchase totals =	$788.58		$858.1538	$858.16	$858.15	$858.20