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	$55.90	4.250%	$58.2758	$58.28	$58.30	$58.30
Purchase #2	$53.71	10.712%	$59.4634	$59.46	$59.45	$59.50
Purchase #3	$192.26	12.249%	$215.8099	$215.81	$215.80	$215.80
Purchase #4	$141.47	7.150%	$151.5851	$151.59	$151.60	$151.60
Purchase #5	$138.40	11.554%	$154.3907	$154.39	$154.40	$154.40
Purchase #6	$245.63	8.687%	$266.9679	$266.97	$266.95	$267.00
Purchase #7	$212.93	13.251%	$241.1454	$241.15	$241.15	$241.10
7 purchase totals =	$1,040.30		$1,147.6382	$1,147.65	$1,147.65	$1,147.70