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	$21.90	4.280%	$22.8373	$22.84	$22.85	$22.80
Purchase #2	$40.56	5.535%	$42.805	$42.81	$42.80	$42.80
Purchase #3	$137.93	6.114%	$146.363	$146.36	$146.35	$146.40
Purchase #4	$73.50	10.303%	$81.0727	$81.07	$81.05	$81.10
Purchase #5	$92.83	6.677%	$99.0283	$99.03	$99.05	$99.00
Purchase #6	$132.32	13.365%	$150.0046	$150.00	$150.00	$150.00
Purchase #7	$176.68	6.871%	$188.8197	$188.82	$188.80	$188.80
7 purchase totals =	$675.72		$730.9306	$730.93	$730.90	$730.90