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	$245.91	13.399%	$278.8595	$278.86	$278.85	$278.90
Purchase #2	$91.96	12.830%	$103.7585	$103.76	$103.75	$103.80
Purchase #3	$220.29	6.148%	$233.8334	$233.83	$233.85	$233.80
Purchase #4	$49.59	9.532%	$54.3169	$54.32	$54.30	$54.30
Purchase #5	$139.53	9.227%	$152.4044	$152.40	$152.40	$152.40
Purchase #6	$52.65	9.225%	$57.507	$57.51	$57.50	$57.50
Purchase #7	$18.66	4.311%	$19.4644	$19.46	$19.45	$19.50
7 purchase totals =	$818.59		$900.1441	$900.14	$900.10	$900.20