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	$35.65	6.186%	$37.8553	$37.86	$37.85	$37.90
Purchase #2	$178.82	13.133%	$202.3044	$202.30	$202.30	$202.30
Purchase #3	$165.73	4.732%	$173.5723	$173.57	$173.55	$173.60
Purchase #4	$109.61	12.772%	$123.6094	$123.61	$123.60	$123.60
Purchase #5	$26.57	5.262%	$27.9681	$27.97	$27.95	$28.00
Purchase #6	$92.69	6.814%	$99.0059	$99.01	$99.00	$99.00
Purchase #7	$127.67	7.637%	$137.4202	$137.42	$137.40	$137.40
7 purchase totals =	$736.74		$801.7356	$801.74	$801.65	$801.80