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	$243.66	12.864%	$275.0044	$275.00	$275.00	$275.00
Purchase #2	$134.73	6.869%	$143.9846	$143.98	$144.00	$144.00
Purchase #3	$39.53	9.551%	$43.3055	$43.31	$43.30	$43.30
Purchase #4	$193.32	5.850%	$204.6292	$204.63	$204.65	$204.60
Purchase #5	$108.59	13.723%	$123.4918	$123.49	$123.50	$123.50
Purchase #6	$227.30	4.770%	$238.1422	$238.14	$238.15	$238.10
Purchase #7	$54.94	4.223%	$57.2601	$57.26	$57.25	$57.30
7 purchase totals =	$1,002.07		$1,085.8178	$1,085.81	$1,085.85	$1,085.80