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	$150.78	4.308%	$157.2756	$157.28	$157.30	$157.30
Purchase #2	$100.93	8.791%	$109.8028	$109.80	$109.80	$109.80
Purchase #3	$70.36	5.816%	$74.4521	$74.45	$74.45	$74.50
Purchase #4	$61.83	9.671%	$67.8096	$67.81	$67.80	$67.80
Purchase #5	$140.72	4.107%	$146.4994	$146.50	$146.50	$146.50
Purchase #6	$223.53	3.439%	$231.2172	$231.22	$231.20	$231.20
Purchase #7	$28.61	12.639%	$32.226	$32.23	$32.25	$32.20
7 purchase totals =	$776.76		$819.2827	$819.29	$819.30	$819.30