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	$17.33	8.440%	$18.7927	$18.79	$18.80	$18.80
Purchase #2	$39.73	13.532%	$45.1063	$45.11	$45.10	$45.10
Purchase #3	$147.51	8.820%	$160.5204	$160.52	$160.50	$160.50
Purchase #4	$80.42	7.329%	$86.314	$86.31	$86.30	$86.30
Purchase #5	$216.93	12.758%	$244.6059	$244.61	$244.60	$244.60
Purchase #6	$52.73	7.256%	$56.5561	$56.56	$56.55	$56.60
Purchase #7	$66.87	13.250%	$75.7303	$75.73	$75.75	$75.70
7 purchase totals =	$621.52		$687.6257	$687.63	$687.60	$687.60