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	$226.95	13.802%	$258.2736	$258.27	$258.25	$258.30
Purchase #2	$139.38	10.615%	$154.1752	$154.18	$154.20	$154.20
Purchase #3	$142.92	7.674%	$153.8877	$153.89	$153.90	$153.90
Purchase #4	$78.74	4.651%	$82.4022	$82.40	$82.40	$82.40
Purchase #5	$228.27	7.131%	$244.5479	$244.55	$244.55	$244.50
Purchase #6	$98.28	11.809%	$109.8859	$109.89	$109.90	$109.90
Purchase #7	$112.99	7.331%	$121.2733	$121.27	$121.25	$121.30
7 purchase totals =	$1,027.53		$1,124.4458	$1,124.45	$1,124.45	$1,124.50