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	$158.67	4.355%	$165.5801	$165.58	$165.60	$165.60
Purchase #2	$123.74	13.358%	$140.2692	$140.27	$140.25	$140.30
Purchase #3	$200.65	10.744%	$222.2078	$222.21	$222.20	$222.20
Purchase #4	$117.79	13.858%	$134.1133	$134.11	$134.10	$134.10
Purchase #5	$91.51	6.588%	$97.5387	$97.54	$97.55	$97.50
Purchase #6	$95.32	4.871%	$99.963	$99.96	$99.95	$100.00
Purchase #7	$114.48	5.243%	$120.4822	$120.48	$120.50	$120.50
7 purchase totals =	$902.16		$980.1543	$980.15	$980.15	$980.20