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	$28.84	11.670%	$32.2056	$32.21	$32.20	$32.20
Purchase #2	$160.38	12.220%	$179.9784	$179.98	$180.00	$180.00
Purchase #3	$144.71	5.150%	$152.1626	$152.16	$152.15	$152.20
Purchase #4	$62.32	8.687%	$67.7337	$67.73	$67.75	$67.70
Purchase #5	$51.54	6.380%	$54.8283	$54.83	$54.85	$54.80
Purchase #6	$91.78	7.491%	$98.6552	$98.66	$98.65	$98.70
Purchase #7	$199.51	12.784%	$225.0154	$225.02	$225.00	$225.00
7 purchase totals =	$739.08		$810.5792	$810.59	$810.60	$810.60