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	$105.69	11.495%	$117.8391	$117.84	$117.85	$117.80
Purchase #2	$180.70	5.303%	$190.2825	$190.28	$190.30	$190.30
Purchase #3	$249.42	6.178%	$264.8292	$264.83	$264.85	$264.80
Purchase #4	$230.76	13.313%	$261.4811	$261.48	$261.50	$261.50
Purchase #5	$152.59	11.451%	$170.0631	$170.06	$170.05	$170.10
Purchase #6	$19.54	11.146%	$21.7179	$21.72	$21.70	$21.70
Purchase #7	$83.63	6.398%	$88.9806	$88.98	$89.00	$89.00
7 purchase totals =	$1,022.33		$1,115.1935	$1,115.19	$1,115.25	$1,115.20