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	$40.44	5.365%	$42.6096	$42.61	$42.60	$42.60
Purchase #2	$126.34	3.148%	$130.3172	$130.32	$130.30	$130.30
Purchase #3	$222.93	6.230%	$236.8185	$236.82	$236.80	$236.80
Purchase #4	$101.36	7.459%	$108.9204	$108.92	$108.90	$108.90
Purchase #5	$43.96	11.308%	$48.931	$48.93	$48.95	$48.90
Purchase #6	$67.37	7.784%	$72.6141	$72.61	$72.60	$72.60
Purchase #7	$68.71	13.493%	$77.981	$77.98	$78.00	$78.00
7 purchase totals =	$671.11		$718.1918	$718.19	$718.15	$718.10