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	$79.59	12.772%	$89.7552	$89.76	$89.75	$89.80
Purchase #2	$6.63	3.678%	$6.8739	$6.87	$6.85	$6.90
Purchase #3	$123.90	5.332%	$130.5063	$130.51	$130.50	$130.50
Purchase #4	$142.88	3.287%	$147.5765	$147.58	$147.60	$147.60
Purchase #5	$162.49	7.865%	$175.2698	$175.27	$175.25	$175.30
Purchase #6	$69.26	11.211%	$77.0247	$77.02	$77.00	$77.00
Purchase #7	$10.57	11.796%	$11.8168	$11.82	$11.80	$11.80
7 purchase totals =	$595.32		$638.8232	$638.83	$638.75	$638.90