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	$132.97	4.759%	$139.298	$139.30	$139.30	$139.30
Purchase #2	$161.27	6.581%	$171.8832	$171.88	$171.90	$171.90
Purchase #3	$88.90	11.390%	$99.0257	$99.03	$99.05	$99.00
Purchase #4	$214.59	13.820%	$244.2463	$244.25	$244.25	$244.20
Purchase #5	$150.57	4.747%	$157.7176	$157.72	$157.70	$157.70
Purchase #6	$37.89	3.349%	$39.1589	$39.16	$39.15	$39.20
Purchase #7	$136.78	10.798%	$151.5495	$151.55	$151.55	$151.50
7 purchase totals =	$922.97		$1,002.8792	$1,002.89	$1,002.90	$1,002.80