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	$141.91	11.563%	$158.3191	$158.32	$158.30	$158.30
Purchase #2	$59.66	11.149%	$66.3115	$66.31	$66.30	$66.30
Purchase #3	$209.74	6.456%	$223.2808	$223.28	$223.30	$223.30
Purchase #4	$61.30	4.504%	$64.061	$64.06	$64.05	$64.10
Purchase #5	$171.59	6.614%	$182.939	$182.94	$182.95	$182.90
Purchase #6	$214.90	13.174%	$243.2109	$243.21	$243.20	$243.20
Purchase #7	$211.38	4.679%	$221.2705	$221.27	$221.25	$221.30
7 purchase totals =	$1,070.48		$1,159.3928	$1,159.39	$1,159.35	$1,159.40