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	$249.79	3.723%	$259.0897	$259.09	$259.10	$259.10
Purchase #2	$180.97	10.454%	$199.8886	$199.89	$199.90	$199.90
Purchase #3	$29.67	10.283%	$32.721	$32.72	$32.70	$32.70
Purchase #4	$131.98	12.528%	$148.5145	$148.51	$148.50	$148.50
Purchase #5	$90.87	11.470%	$101.2928	$101.29	$101.30	$101.30
Purchase #6	$146.34	7.745%	$157.674	$157.67	$157.65	$157.70
Purchase #7	$120.66	5.664%	$127.4942	$127.49	$127.50	$127.50
7 purchase totals =	$950.28		$1,026.6748	$1,026.66	$1,026.65	$1,026.70