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	$225.79	8.323%	$244.5825	$244.58	$244.60	$244.60
Purchase #2	$146.78	9.417%	$160.6023	$160.60	$160.60	$160.60
Purchase #3	$26.30	4.541%	$27.4943	$27.49	$27.50	$27.50
Purchase #4	$49.64	6.483%	$52.8582	$52.86	$52.85	$52.90
Purchase #5	$130.65	9.235%	$142.7155	$142.72	$142.70	$142.70
Purchase #6	$41.81	4.159%	$43.5489	$43.55	$43.55	$43.50
Purchase #7	$185.70	3.290%	$191.8095	$191.81	$191.80	$191.80
7 purchase totals =	$806.67		$863.6112	$863.61	$863.60	$863.60