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	$103.61	8.610%	$112.5308	$112.53	$112.55	$112.50
Purchase #2	$100.82	7.740%	$108.6235	$108.62	$108.60	$108.60
Purchase #3	$69.74	11.543%	$77.7901	$77.79	$77.80	$77.80
Purchase #4	$109.78	12.326%	$123.3115	$123.31	$123.30	$123.30
Purchase #5	$157.83	4.165%	$164.4036	$164.40	$164.40	$164.40
Purchase #6	$82.62	10.512%	$91.305	$91.31	$91.30	$91.30
Purchase #7	$113.77	13.847%	$129.5237	$129.52	$129.50	$129.50
7 purchase totals =	$738.17		$807.4882	$807.48	$807.45	$807.40