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	$225.40	10.612%	$249.3194	$249.32	$249.30	$249.30
Purchase #2	$54.46	4.245%	$56.7718	$56.77	$56.75	$56.80
Purchase #3	$201.49	7.159%	$215.9147	$215.91	$215.90	$215.90
Purchase #4	$32.31	4.667%	$33.8179	$33.82	$33.80	$33.80
Purchase #5	$84.25	12.153%	$94.4889	$94.49	$94.50	$94.50
Purchase #6	$145.87	13.500%	$165.5625	$165.56	$165.55	$165.60
Purchase #7	$249.66	13.126%	$282.4304	$282.43	$282.45	$282.40
7 purchase totals =	$993.44		$1,098.3056	$1,098.30	$1,098.25	$1,098.30