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	$90.48	4.845%	$94.8638	$94.86	$94.85	$94.90
Purchase #2	$203.87	8.620%	$221.4436	$221.44	$221.45	$221.40
Purchase #3	$77.99	5.283%	$82.1102	$82.11	$82.10	$82.10
Purchase #4	$146.87	10.429%	$162.1871	$162.19	$162.20	$162.20
Purchase #5	$12.30	12.282%	$13.8107	$13.81	$13.80	$13.80
Purchase #6	$18.79	8.729%	$20.4302	$20.43	$20.45	$20.40
Purchase #7	$172.43	7.610%	$185.5519	$185.55	$185.55	$185.60
7 purchase totals =	$722.73		$780.3975	$780.39	$780.40	$780.40