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	$166.66	5.380%	$175.6263	$175.63	$175.65	$175.60
Purchase #2	$108.47	9.550%	$118.8289	$118.83	$118.85	$118.80
Purchase #3	$227.98	3.847%	$236.7504	$236.75	$236.75	$236.80
Purchase #4	$100.31	3.524%	$103.8449	$103.84	$103.85	$103.80
Purchase #5	$79.63	5.124%	$83.7102	$83.71	$83.70	$83.70
Purchase #6	$98.60	5.251%	$103.7775	$103.78	$103.80	$103.80
Purchase #7	$169.83	8.700%	$184.6052	$184.61	$184.60	$184.60
7 purchase totals =	$951.48		$1,007.1434	$1,007.15	$1,007.20	$1,007.10