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	$130.70	7.646%	$140.6933	$140.69	$140.70	$140.70
Purchase #2	$243.56	3.802%	$252.8202	$252.82	$252.80	$252.80
Purchase #3	$39.99	6.188%	$42.4646	$42.46	$42.45	$42.50
Purchase #4	$99.41	4.616%	$103.9988	$104.00	$104.00	$104.00
Purchase #5	$123.49	12.244%	$138.6101	$138.61	$138.60	$138.60
Purchase #6	$57.28	7.194%	$61.4007	$61.40	$61.40	$61.40
Purchase #7	$26.59	3.317%	$27.472	$27.47	$27.45	$27.50
7 purchase totals =	$721.02		$767.4597	$767.45	$767.40	$767.50