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	$89.33	11.442%	$99.5511	$99.55	$99.55	$99.60
Purchase #2	$53.76	8.601%	$58.3839	$58.38	$58.40	$58.40
Purchase #3	$104.76	3.169%	$108.0798	$108.08	$108.10	$108.10
Purchase #4	$135.46	5.802%	$143.3194	$143.32	$143.30	$143.30
Purchase #5	$136.77	4.392%	$142.7769	$142.78	$142.80	$142.80
Purchase #6	$225.45	12.513%	$253.6606	$253.66	$253.65	$253.70
Purchase #7	$27.48	8.739%	$29.8815	$29.88	$29.90	$29.90
7 purchase totals =	$773.01		$835.6532	$835.65	$835.70	$835.80