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	$93.87	9.147%	$102.4563	$102.46	$102.45	$102.50
Purchase #2	$57.78	6.475%	$61.5213	$61.52	$61.50	$61.50
Purchase #3	$113.71	8.592%	$123.48	$123.48	$123.50	$123.50
Purchase #4	$211.85	3.615%	$219.5084	$219.51	$219.50	$219.50
Purchase #5	$30.28	3.457%	$31.3268	$31.33	$31.35	$31.30
Purchase #6	$179.95	4.507%	$188.0603	$188.06	$188.05	$188.10
Purchase #7	$243.65	4.869%	$255.5133	$255.51	$255.50	$255.50
7 purchase totals =	$931.09		$981.8664	$981.87	$981.85	$981.90