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	$170.70	7.412%	$183.3523	$183.35	$183.35	$183.40
Purchase #2	$194.47	9.865%	$213.6545	$213.65	$213.65	$213.70
Purchase #3	$45.76	6.609%	$48.7843	$48.78	$48.80	$48.80
Purchase #4	$143.41	5.737%	$151.6374	$151.64	$151.65	$151.60
Purchase #5	$20.64	5.797%	$21.8365	$21.84	$21.85	$21.80
Purchase #6	$126.66	3.776%	$131.4427	$131.44	$131.45	$131.40
Purchase #7	$72.63	13.166%	$82.1925	$82.19	$82.20	$82.20
7 purchase totals =	$774.27		$832.9002	$832.89	$832.95	$832.90