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	$25.51	8.165%	$27.5929	$27.59	$27.60	$27.60
Purchase #2	$34.46	8.450%	$37.3719	$37.37	$37.35	$37.40
Purchase #3	$156.93	13.823%	$178.6224	$178.62	$178.60	$178.60
Purchase #4	$77.76	13.519%	$88.2724	$88.27	$88.25	$88.30
Purchase #5	$228.30	5.734%	$241.3907	$241.39	$241.40	$241.40
Purchase #6	$221.41	10.171%	$243.9296	$243.93	$243.95	$243.90
Purchase #7	$45.33	3.271%	$46.8127	$46.81	$46.80	$46.80
7 purchase totals =	$789.70		$863.9926	$863.98	$863.95	$864.00