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	$123.32	3.607%	$127.7682	$127.77	$127.75	$127.80
Purchase #2	$26.59	4.418%	$27.7647	$27.76	$27.75	$27.80
Purchase #3	$208.34	7.645%	$224.2676	$224.27	$224.25	$224.30
Purchase #4	$41.99	10.163%	$46.2574	$46.26	$46.25	$46.30
Purchase #5	$42.63	3.616%	$44.1715	$44.17	$44.15	$44.20
Purchase #6	$106.83	4.539%	$111.679	$111.68	$111.70	$111.70
Purchase #7	$69.59	6.256%	$73.9436	$73.94	$73.95	$73.90
7 purchase totals =	$619.29		$655.8520	$655.85	$655.80	$656.00