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	$243.40	12.610%	$274.0927	$274.09	$274.10	$274.10
Purchase #2	$61.46	8.271%	$66.5434	$66.54	$66.55	$66.50
Purchase #3	$100.67	10.308%	$111.0471	$111.05	$111.05	$111.00
Purchase #4	$101.39	7.742%	$109.2396	$109.24	$109.25	$109.20
Purchase #5	$183.76	12.556%	$206.8329	$206.83	$206.85	$206.80
Purchase #6	$207.38	13.104%	$234.5551	$234.56	$234.55	$234.60
Purchase #7	$47.45	4.593%	$49.6294	$49.63	$49.65	$49.60
7 purchase totals =	$945.51		$1,051.9402	$1,051.94	$1,052.00	$1,051.80