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	$43.75	5.431%	$46.1261	$46.13	$46.15	$46.10
Purchase #2	$124.77	11.537%	$139.1647	$139.16	$139.15	$139.20
Purchase #3	$132.51	11.456%	$147.6903	$147.69	$147.70	$147.70
Purchase #4	$48.71	11.802%	$54.4588	$54.46	$54.45	$54.50
Purchase #5	$124.38	7.445%	$133.6401	$133.64	$133.65	$133.60
Purchase #6	$139.82	9.114%	$152.5632	$152.56	$152.55	$152.60
Purchase #7	$171.79	10.611%	$190.0186	$190.02	$190.00	$190.00
7 purchase totals =	$785.73		$863.6618	$863.66	$863.65	$863.70