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	$93.53	7.371%	$100.4241	$100.42	$100.40	$100.40
Purchase #2	$183.49	9.342%	$200.6316	$200.63	$200.65	$200.60
Purchase #3	$16.82	7.527%	$18.086	$18.09	$18.10	$18.10
Purchase #4	$178.53	8.505%	$193.714	$193.71	$193.70	$193.70
Purchase #5	$163.62	13.445%	$185.6187	$185.62	$185.60	$185.60
Purchase #6	$91.71	13.570%	$104.155	$104.16	$104.15	$104.20
Purchase #7	$82.79	10.378%	$91.3819	$91.38	$91.40	$91.40
7 purchase totals =	$810.49		$894.0113	$894.01	$894.00	$894.00