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	$89.42	11.415%	$99.6273	$99.63	$99.65	$99.60
Purchase #2	$172.87	10.507%	$191.0335	$191.03	$191.05	$191.00
Purchase #3	$49.70	12.793%	$56.0581	$56.06	$56.05	$56.10
Purchase #4	$27.46	13.429%	$31.1476	$31.15	$31.15	$31.10
Purchase #5	$160.40	12.495%	$180.442	$180.44	$180.45	$180.40
Purchase #6	$94.50	6.486%	$100.6293	$100.63	$100.65	$100.60
Purchase #7	$63.69	12.285%	$71.5143	$71.51	$71.50	$71.50
7 purchase totals =	$658.04		$730.4521	$730.45	$730.50	$730.30