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	$85.48	4.821%	$89.601	$89.60	$89.60	$89.60
Purchase #2	$20.89	12.453%	$23.4914	$23.49	$23.50	$23.50
Purchase #3	$22.72	8.319%	$24.6101	$24.61	$24.60	$24.60
Purchase #4	$13.74	13.649%	$15.6154	$15.62	$15.60	$15.60
Purchase #5	$172.95	4.755%	$181.1738	$181.17	$181.15	$181.20
Purchase #6	$46.31	12.279%	$51.9964	$52.00	$52.00	$52.00
Purchase #7	$63.63	7.709%	$68.5352	$68.54	$68.55	$68.50
7 purchase totals =	$425.72		$455.0233	$455.03	$455.00	$455.00