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	$94.73	3.616%	$98.1554	$98.16	$98.15	$98.20
Purchase #2	$50.33	13.777%	$57.264	$57.26	$57.25	$57.30
Purchase #3	$98.40	11.473%	$109.6894	$109.69	$109.70	$109.70
Purchase #4	$96.62	4.359%	$100.8317	$100.83	$100.85	$100.80
Purchase #5	$130.72	6.560%	$139.2952	$139.30	$139.30	$139.30
Purchase #6	$250.78	8.831%	$272.9264	$272.93	$272.95	$272.90
Purchase #7	$24.33	12.641%	$27.4056	$27.41	$27.40	$27.40
7 purchase totals =	$745.91		$805.5677	$805.58	$805.60	$805.60