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	$88.96	5.169%	$93.5583	$93.56	$93.55	$93.60
Purchase #2	$79.91	13.409%	$90.6251	$90.63	$90.65	$90.60
Purchase #3	$43.32	5.304%	$45.6177	$45.62	$45.60	$45.60
Purchase #4	$55.74	11.740%	$62.2839	$62.28	$62.30	$62.30
Purchase #5	$8.34	6.472%	$8.8798	$8.88	$8.90	$8.90
Purchase #6	$134.75	4.511%	$140.8286	$140.83	$140.85	$140.80
Purchase #7	$176.72	6.255%	$187.7738	$187.77	$187.75	$187.80
7 purchase totals =	$587.74		$629.5672	$629.57	$629.60	$629.60