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	$70.64	10.554%	$78.0953	$78.10	$78.10	$78.10
Purchase #2	$83.89	7.557%	$90.2296	$90.23	$90.25	$90.20
Purchase #3	$173.33	4.466%	$181.0709	$181.07	$181.05	$181.10
Purchase #4	$148.56	11.376%	$165.4602	$165.46	$165.45	$165.50
Purchase #5	$51.26	13.180%	$58.0161	$58.02	$58.00	$58.00
Purchase #6	$23.60	5.829%	$24.9756	$24.98	$25.00	$25.00
Purchase #7	$194.86	10.371%	$215.0689	$215.07	$215.05	$215.10
7 purchase totals =	$746.14		$812.9166	$812.93	$812.90	$813.00