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	$69.93	6.411%	$74.4132	$74.41	$74.40	$74.40
Purchase #2	$112.89	13.155%	$127.7407	$127.74	$127.75	$127.70
Purchase #3	$198.38	9.322%	$216.873	$216.87	$216.85	$216.90
Purchase #4	$99.82	5.661%	$105.4708	$105.47	$105.45	$105.50
Purchase #5	$130.91	9.432%	$143.2574	$143.26	$143.25	$143.30
Purchase #6	$76.76	4.396%	$80.1344	$80.13	$80.15	$80.10
Purchase #7	$88.69	7.418%	$95.269	$95.27	$95.25	$95.30
7 purchase totals =	$777.38		$843.1585	$843.15	$843.10	$843.20