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	$6.74	8.699%	$7.3263	$7.33	$7.35	$7.30
Purchase #2	$58.99	3.836%	$61.2529	$61.25	$61.25	$61.30
Purchase #3	$116.25	12.147%	$130.3709	$130.37	$130.35	$130.40
Purchase #4	$133.83	4.332%	$139.6275	$139.63	$139.65	$139.60
Purchase #5	$19.93	9.167%	$21.757	$21.76	$21.75	$21.80
Purchase #6	$110.91	3.139%	$114.3915	$114.39	$114.40	$114.40
Purchase #7	$167.61	10.867%	$185.8242	$185.82	$185.80	$185.80
7 purchase totals =	$614.26		$660.5503	$660.55	$660.55	$660.60