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	$38.45	6.862%	$41.0884	$41.09	$41.10	$41.10
Purchase #2	$77.75	12.191%	$87.2285	$87.23	$87.25	$87.20
Purchase #3	$83.97	7.606%	$90.3568	$90.36	$90.35	$90.40
Purchase #4	$94.63	5.172%	$99.5243	$99.52	$99.50	$99.50
Purchase #5	$11.46	3.371%	$11.8463	$11.85	$11.85	$11.80
Purchase #6	$60.57	8.623%	$65.793	$65.79	$65.80	$65.80
Purchase #7	$52.38	9.643%	$57.431	$57.43	$57.45	$57.40
7 purchase totals =	$419.21		$453.2683	$453.27	$453.30	$453.20