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	$57.37	3.728%	$59.5088	$59.51	$59.50	$59.50
Purchase #2	$232.76	12.789%	$262.5277	$262.53	$262.55	$262.50
Purchase #3	$89.44	9.807%	$98.2114	$98.21	$98.20	$98.20
Purchase #4	$125.51	11.269%	$139.6537	$139.65	$139.65	$139.70
Purchase #5	$34.47	13.600%	$39.1579	$39.16	$39.15	$39.20
Purchase #6	$137.28	5.192%	$144.4076	$144.41	$144.40	$144.40
Purchase #7	$144.39	6.413%	$153.6497	$153.65	$153.65	$153.60
7 purchase totals =	$821.22		$897.1168	$897.12	$897.10	$897.10