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	$19.69	9.375%	$21.5359	$21.54	$21.55	$21.50
Purchase #2	$107.47	4.796%	$112.6243	$112.62	$112.60	$112.60
Purchase #3	$199.40	8.441%	$216.2314	$216.23	$216.25	$216.20
Purchase #4	$38.26	12.253%	$42.948	$42.95	$42.95	$42.90
Purchase #5	$146.30	8.408%	$158.6009	$158.60	$158.60	$158.60
Purchase #6	$144.49	11.396%	$160.9561	$160.96	$160.95	$161.00
Purchase #7	$133.80	6.459%	$142.4421	$142.44	$142.45	$142.40
7 purchase totals =	$789.41		$855.3387	$855.34	$855.35	$855.20