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	$80.33	13.443%	$91.1288	$91.13	$91.15	$91.10
Purchase #2	$138.32	7.630%	$148.8738	$148.87	$148.85	$148.90
Purchase #3	$73.75	12.751%	$83.1539	$83.15	$83.15	$83.20
Purchase #4	$39.27	11.151%	$43.649	$43.65	$43.65	$43.60
Purchase #5	$221.75	8.133%	$239.7849	$239.78	$239.80	$239.80
Purchase #6	$10.69	6.568%	$11.3921	$11.39	$11.40	$11.40
Purchase #7	$199.69	6.591%	$212.8516	$212.85	$212.85	$212.90
7 purchase totals =	$763.80		$830.8341	$830.82	$830.85	$830.90