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	$37.52	8.299%	$40.6338	$40.63	$40.65	$40.60
Purchase #2	$74.38	10.484%	$82.178	$82.18	$82.20	$82.20
Purchase #3	$139.90	3.258%	$144.4579	$144.46	$144.45	$144.50
Purchase #4	$60.46	8.134%	$65.3778	$65.38	$65.40	$65.40
Purchase #5	$225.40	11.289%	$250.8454	$250.85	$250.85	$250.80
Purchase #6	$23.61	8.402%	$25.5937	$25.59	$25.60	$25.60
Purchase #7	$222.92	12.244%	$250.2143	$250.21	$250.20	$250.20
7 purchase totals =	$784.19		$859.3009	$859.30	$859.35	$859.30