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	$123.39	12.784%	$139.1642	$139.16	$139.15	$139.20
Purchase #2	$128.86	5.790%	$136.321	$136.32	$136.30	$136.30
Purchase #3	$43.60	9.822%	$47.8824	$47.88	$47.90	$47.90
Purchase #4	$137.50	6.275%	$146.1281	$146.13	$146.15	$146.10
Purchase #5	$114.58	13.600%	$130.1629	$130.16	$130.15	$130.20
Purchase #6	$147.42	12.690%	$166.1276	$166.13	$166.15	$166.10
Purchase #7	$42.79	4.361%	$44.6561	$44.66	$44.65	$44.70
7 purchase totals =	$738.14		$810.4423	$810.44	$810.45	$810.50