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	$45.31	13.162%	$51.2737	$51.27	$51.25	$51.30
Purchase #2	$248.27	12.696%	$279.7904	$279.79	$279.80	$279.80
Purchase #3	$91.39	13.173%	$103.4288	$103.43	$103.45	$103.40
Purchase #4	$93.40	4.727%	$97.815	$97.82	$97.80	$97.80
Purchase #5	$115.53	6.584%	$123.1365	$123.14	$123.15	$123.10
Purchase #6	$52.88	5.571%	$55.8259	$55.83	$55.85	$55.80
Purchase #7	$149.28	7.262%	$160.1207	$160.12	$160.10	$160.10
7 purchase totals =	$796.06		$871.3910	$871.40	$871.40	$871.30