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	$123.95	11.587%	$138.3121	$138.31	$138.30	$138.30
Purchase #2	$99.95	12.436%	$112.3798	$112.38	$112.40	$112.40
Purchase #3	$182.77	4.533%	$191.055	$191.06	$191.05	$191.10
Purchase #4	$100.34	4.699%	$105.055	$105.06	$105.05	$105.10
Purchase #5	$151.28	9.439%	$165.5593	$165.56	$165.55	$165.60
Purchase #6	$89.26	8.551%	$96.8926	$96.89	$96.90	$96.90
Purchase #7	$87.77	10.145%	$96.6743	$96.67	$96.65	$96.70
7 purchase totals =	$835.32		$905.9281	$905.93	$905.90	$906.10