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	$216.64	12.168%	$243.0008	$243.00	$243.00	$243.00
Purchase #2	$112.26	6.105%	$119.1135	$119.11	$119.10	$119.10
Purchase #3	$177.45	13.210%	$200.8911	$200.89	$200.90	$200.90
Purchase #4	$250.78	11.178%	$278.8122	$278.81	$278.80	$278.80
Purchase #5	$59.39	7.112%	$63.6138	$63.61	$63.60	$63.60
Purchase #6	$64.72	11.765%	$72.3343	$72.33	$72.35	$72.30
Purchase #7	$137.84	3.549%	$142.7319	$142.73	$142.75	$142.70
7 purchase totals =	$1,019.08		$1,120.4976	$1,120.48	$1,120.50	$1,120.40