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	$38.47	10.805%	$42.6267	$42.63	$42.65	$42.60
Purchase #2	$84.77	4.810%	$88.8474	$88.85	$88.85	$88.80
Purchase #3	$245.91	10.463%	$271.6396	$271.64	$271.65	$271.60
Purchase #4	$26.53	6.814%	$28.3378	$28.34	$28.35	$28.30
Purchase #5	$148.93	6.604%	$158.7653	$158.77	$158.75	$158.80
Purchase #6	$90.52	9.788%	$99.3801	$99.38	$99.40	$99.40
Purchase #7	$231.47	5.306%	$243.7518	$243.75	$243.75	$243.80
7 purchase totals =	$866.60		$933.3487	$933.36	$933.40	$933.30