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	$134.88	10.102%	$148.5056	$148.51	$148.50	$148.50
Purchase #2	$228.66	3.583%	$236.8529	$236.85	$236.85	$236.90
Purchase #3	$109.58	13.525%	$124.4007	$124.40	$124.40	$124.40
Purchase #4	$168.62	6.542%	$179.6511	$179.65	$179.65	$179.70
Purchase #5	$93.46	7.588%	$100.5517	$100.55	$100.55	$100.60
Purchase #6	$189.75	11.478%	$211.5295	$211.53	$211.55	$211.50
Purchase #7	$86.81	4.463%	$90.6843	$90.68	$90.70	$90.70
7 purchase totals =	$1,011.76		$1,092.1758	$1,092.17	$1,092.20	$1,092.30