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	$207.94	10.199%	$229.1478	$229.15	$229.15	$229.10
Purchase #2	$150.27	12.105%	$168.4602	$168.46	$168.45	$168.50
Purchase #3	$102.68	4.351%	$107.1476	$107.15	$107.15	$107.10
Purchase #4	$9.72	11.770%	$10.864	$10.86	$10.85	$10.90
Purchase #5	$90.73	6.715%	$96.8225	$96.82	$96.80	$96.80
Purchase #6	$240.54	11.227%	$267.5454	$267.55	$267.55	$267.50
Purchase #7	$91.42	9.674%	$100.264	$100.26	$100.25	$100.30
7 purchase totals =	$893.30		$980.2515	$980.25	$980.20	$980.20