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	$131.30	12.631%	$147.8845	$147.88	$147.90	$147.90
Purchase #2	$49.59	8.148%	$53.6306	$53.63	$53.65	$53.60
Purchase #3	$155.32	7.146%	$166.4192	$166.42	$166.40	$166.40
Purchase #4	$52.31	11.835%	$58.5009	$58.50	$58.50	$58.50
Purchase #5	$18.85	7.339%	$20.2334	$20.23	$20.25	$20.20
Purchase #6	$32.59	3.648%	$33.7789	$33.78	$33.80	$33.80
Purchase #7	$18.49	6.743%	$19.7368	$19.74	$19.75	$19.70
7 purchase totals =	$458.45		$500.1843	$500.18	$500.25	$500.10