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	$49.78	9.495%	$54.5066	$54.51	$54.50	$54.50
Purchase #2	$132.38	10.578%	$146.3832	$146.38	$146.40	$146.40
Purchase #3	$146.75	3.199%	$151.4445	$151.44	$151.45	$151.40
Purchase #4	$218.50	11.741%	$244.1541	$244.15	$244.15	$244.20
Purchase #5	$68.49	4.632%	$71.6625	$71.66	$71.65	$71.70
Purchase #6	$71.50	11.179%	$79.493	$79.49	$79.50	$79.50
Purchase #7	$83.93	12.443%	$94.3734	$94.37	$94.35	$94.40
7 purchase totals =	$771.33		$842.0173	$842.00	$842.00	$842.10