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	$106.30	11.848%	$118.8944	$118.89	$118.90	$118.90
Purchase #2	$53.79	12.186%	$60.3448	$60.34	$60.35	$60.30
Purchase #3	$141.33	10.381%	$156.0015	$156.00	$156.00	$156.00
Purchase #4	$210.39	7.192%	$225.5212	$225.52	$225.50	$225.50
Purchase #5	$134.63	5.732%	$142.347	$142.35	$142.35	$142.30
Purchase #6	$217.87	10.539%	$240.8313	$240.83	$240.85	$240.80
Purchase #7	$56.68	4.316%	$59.1263	$59.13	$59.15	$59.10
7 purchase totals =	$920.99		$1,003.0665	$1,003.06	$1,003.10	$1,002.90