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	$91.96	12.465%	$103.4228	$103.42	$103.40	$103.40
Purchase #2	$17.46	10.173%	$19.2362	$19.24	$19.25	$19.20
Purchase #3	$231.25	8.444%	$250.7768	$250.78	$250.80	$250.80
Purchase #4	$236.97	10.588%	$262.0604	$262.06	$262.05	$262.10
Purchase #5	$20.33	12.289%	$22.8284	$22.83	$22.85	$22.80
Purchase #6	$118.71	3.695%	$123.0963	$123.10	$123.10	$123.10
Purchase #7	$31.61	4.224%	$32.9452	$32.95	$32.95	$32.90
7 purchase totals =	$748.29		$814.3661	$814.38	$814.40	$814.30