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	$100.53	12.155%	$112.7494	$112.75	$112.75	$112.70
Purchase #2	$45.59	8.797%	$49.6006	$49.60	$49.60	$49.60
Purchase #3	$233.44	7.784%	$251.611	$251.61	$251.60	$251.60
Purchase #4	$93.55	6.354%	$99.4942	$99.49	$99.50	$99.50
Purchase #5	$79.37	3.462%	$82.1178	$82.12	$82.10	$82.10
Purchase #6	$61.35	10.535%	$67.8132	$67.81	$67.80	$67.80
Purchase #7	$174.28	7.449%	$187.2621	$187.26	$187.25	$187.30
7 purchase totals =	$788.11		$850.6483	$850.64	$850.60	$850.60