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	$190.40	7.271%	$204.244	$204.24	$204.25	$204.20
Purchase #2	$211.56	10.522%	$233.8203	$233.82	$233.80	$233.80
Purchase #3	$93.26	6.221%	$99.0617	$99.06	$99.05	$99.10
Purchase #4	$40.25	5.633%	$42.5173	$42.52	$42.50	$42.50
Purchase #5	$11.87	13.681%	$13.4939	$13.49	$13.50	$13.50
Purchase #6	$169.60	7.218%	$181.8417	$181.84	$181.85	$181.80
Purchase #7	$176.40	5.344%	$185.8268	$185.83	$185.85	$185.80
7 purchase totals =	$893.34		$960.8057	$960.80	$960.80	$960.70