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	$247.89	9.102%	$270.4529	$270.45	$270.45	$270.50
Purchase #2	$112.58	10.348%	$124.2298	$124.23	$124.25	$124.20
Purchase #3	$121.67	12.243%	$136.5661	$136.57	$136.55	$136.60
Purchase #4	$209.31	9.196%	$228.5581	$228.56	$228.55	$228.60
Purchase #5	$120.77	5.847%	$127.8314	$127.83	$127.85	$127.80
Purchase #6	$179.96	4.389%	$187.8584	$187.86	$187.85	$187.90
Purchase #7	$53.26	6.496%	$56.7198	$56.72	$56.70	$56.70
7 purchase totals =	$1,045.44		$1,132.2165	$1,132.22	$1,132.20	$1,132.30