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	$40.80	4.454%	$42.6172	$42.62	$42.60	$42.60
Purchase #2	$156.63	10.632%	$173.2829	$173.28	$173.30	$173.30
Purchase #3	$51.54	13.572%	$58.535	$58.54	$58.55	$58.50
Purchase #4	$146.85	9.515%	$160.8228	$160.82	$160.80	$160.80
Purchase #5	$99.32	5.318%	$104.6018	$104.60	$104.60	$104.60
Purchase #6	$178.28	5.110%	$187.3901	$187.39	$187.40	$187.40
Purchase #7	$7.40	5.294%	$7.7918	$7.79	$7.80	$7.80
7 purchase totals =	$680.82		$735.0416	$735.04	$735.05	$735.00