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	$244.80	11.428%	$272.7757	$272.78	$272.80	$272.80
Purchase #2	$51.97	4.143%	$54.1231	$54.12	$54.10	$54.10
Purchase #3	$40.81	10.293%	$45.0106	$45.01	$45.00	$45.00
Purchase #4	$80.78	11.760%	$90.2797	$90.28	$90.30	$90.30
Purchase #5	$33.42	6.811%	$35.6962	$35.70	$35.70	$35.70
Purchase #6	$247.78	10.144%	$272.9148	$272.91	$272.90	$272.90
Purchase #7	$61.37	11.181%	$68.2318	$68.23	$68.25	$68.20
7 purchase totals =	$760.93		$839.0319	$839.03	$839.05	$839.00