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	$150.56	11.225%	$167.4604	$167.46	$167.45	$167.50
Purchase #2	$25.56	11.728%	$28.5577	$28.56	$28.55	$28.60
Purchase #3	$233.85	13.213%	$264.7486	$264.75	$264.75	$264.70
Purchase #4	$45.54	6.767%	$48.6217	$48.62	$48.60	$48.60
Purchase #5	$58.84	4.867%	$61.7037	$61.70	$61.70	$61.70
Purchase #6	$216.68	12.519%	$243.8062	$243.81	$243.80	$243.80
Purchase #7	$23.69	3.645%	$24.5535	$24.55	$24.55	$24.60
7 purchase totals =	$754.72		$839.4518	$839.45	$839.40	$839.50