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	$105.43	5.142%	$110.8512	$110.85	$110.85	$110.90
Purchase #2	$236.73	8.485%	$256.8165	$256.82	$256.80	$256.80
Purchase #3	$115.71	10.160%	$127.4661	$127.47	$127.45	$127.50
Purchase #4	$134.48	11.325%	$149.7099	$149.71	$149.70	$149.70
Purchase #5	$163.98	5.426%	$172.8776	$172.88	$172.90	$172.90
Purchase #6	$82.46	5.297%	$86.8279	$86.83	$86.85	$86.80
Purchase #7	$32.74	9.660%	$35.9027	$35.90	$35.90	$35.90
7 purchase totals =	$871.53		$940.4519	$940.46	$940.45	$940.50