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	$42.99	4.413%	$44.8871	$44.89	$44.90	$44.90
Purchase #2	$116.53	9.751%	$127.8928	$127.89	$127.90	$127.90
Purchase #3	$15.72	5.385%	$16.5665	$16.57	$16.55	$16.60
Purchase #4	$15.80	9.304%	$17.27	$17.27	$17.25	$17.30
Purchase #5	$88.52	9.446%	$96.8816	$96.88	$96.90	$96.90
Purchase #6	$206.75	6.343%	$219.8642	$219.86	$219.85	$219.90
Purchase #7	$150.25	11.219%	$167.1065	$167.11	$167.10	$167.10
7 purchase totals =	$636.56		$690.4687	$690.47	$690.45	$690.60