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	$232.77	7.752%	$250.8143	$250.81	$250.80	$250.80
Purchase #2	$158.69	12.781%	$178.9722	$178.97	$178.95	$179.00
Purchase #3	$77.42	7.479%	$83.2102	$83.21	$83.20	$83.20
Purchase #4	$37.55	12.863%	$42.3801	$42.38	$42.40	$42.40
Purchase #5	$32.77	11.731%	$36.6142	$36.61	$36.60	$36.60
Purchase #6	$122.38	8.162%	$132.3687	$132.37	$132.35	$132.40
Purchase #7	$98.81	4.293%	$103.0519	$103.05	$103.05	$103.10
7 purchase totals =	$760.39		$827.4116	$827.40	$827.35	$827.50