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	$28.46	5.278%	$29.9621	$29.96	$29.95	$30.00
Purchase #2	$47.73	5.847%	$50.5208	$50.52	$50.50	$50.50
Purchase #3	$16.26	13.551%	$18.4634	$18.46	$18.45	$18.50
Purchase #4	$36.91	13.836%	$42.0169	$42.02	$42.00	$42.00
Purchase #5	$48.60	9.609%	$53.27	$53.27	$53.25	$53.30
Purchase #6	$6.39	11.330%	$7.114	$7.11	$7.10	$7.10
Purchase #7	$35.55	6.234%	$37.7662	$37.77	$37.75	$37.80
7 purchase totals =	$219.90		$239.1134	$239.11	$239.00	$239.20