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	$53.61	10.275%	$59.1184	$59.12	$59.10	$59.10
Purchase #2	$93.77	3.163%	$96.7359	$96.74	$96.75	$96.70
Purchase #3	$94.89	7.731%	$102.2259	$102.23	$102.25	$102.20
Purchase #4	$32.36	9.594%	$35.4646	$35.46	$35.45	$35.50
Purchase #5	$216.43	4.321%	$225.7819	$225.78	$225.80	$225.80
Purchase #6	$62.82	6.260%	$66.7525	$66.75	$66.75	$66.80
Purchase #7	$54.31	6.603%	$57.8961	$57.90	$57.90	$57.90
7 purchase totals =	$608.19		$643.9753	$643.98	$644.00	$644.00