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	$243.90	5.226%	$256.6462	$256.65	$256.65	$256.60
Purchase #2	$175.41	6.795%	$187.3291	$187.33	$187.35	$187.30
Purchase #3	$79.41	12.469%	$89.3116	$89.31	$89.30	$89.30
Purchase #4	$240.84	9.720%	$264.2496	$264.25	$264.25	$264.20
Purchase #5	$134.82	7.432%	$144.8398	$144.84	$144.85	$144.80
Purchase #6	$81.89	8.175%	$88.5845	$88.58	$88.60	$88.60
Purchase #7	$224.93	10.461%	$248.4599	$248.46	$248.45	$248.50
7 purchase totals =	$1,181.20		$1,279.4207	$1,279.42	$1,279.45	$1,279.30