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	$100.25	12.461%	$112.7422	$112.74	$112.75	$112.70
Purchase #2	$220.54	10.174%	$242.9777	$242.98	$243.00	$243.00
Purchase #3	$91.51	12.588%	$103.0293	$103.03	$103.05	$103.00
Purchase #4	$18.81	12.221%	$21.1088	$21.11	$21.10	$21.10
Purchase #5	$220.99	10.169%	$243.4625	$243.46	$243.45	$243.50
Purchase #6	$7.86	7.785%	$8.4719	$8.47	$8.45	$8.50
Purchase #7	$250.80	8.400%	$271.8672	$271.87	$271.85	$271.90
7 purchase totals =	$910.76		$1,003.6596	$1,003.66	$1,003.65	$1,003.70