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	$22.56	6.494%	$24.025	$24.03	$24.05	$24.00
Purchase #2	$80.34	10.658%	$88.9026	$88.90	$88.90	$88.90
Purchase #3	$196.82	13.839%	$224.0579	$224.06	$224.05	$224.10
Purchase #4	$29.82	10.779%	$33.0343	$33.03	$33.05	$33.00
Purchase #5	$127.42	5.218%	$134.0688	$134.07	$134.05	$134.10
Purchase #6	$219.83	10.353%	$242.589	$242.59	$242.60	$242.60
Purchase #7	$33.69	10.290%	$37.1567	$37.16	$37.15	$37.20
7 purchase totals =	$710.48		$783.8343	$783.84	$783.85	$783.90