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	$174.99	4.736%	$183.2775	$183.28	$183.30	$183.30
Purchase #2	$151.40	4.232%	$157.8072	$157.81	$157.80	$157.80
Purchase #3	$88.57	13.786%	$100.7803	$100.78	$100.80	$100.80
Purchase #4	$74.30	3.461%	$76.8715	$76.87	$76.85	$76.90
Purchase #5	$42.56	9.300%	$46.5181	$46.52	$46.50	$46.50
Purchase #6	$136.55	10.290%	$150.601	$150.60	$150.60	$150.60
Purchase #7	$171.94	11.404%	$191.548	$191.55	$191.55	$191.50
7 purchase totals =	$840.31		$907.4036	$907.41	$907.40	$907.40