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	$110.26	12.601%	$124.1539	$124.15	$124.15	$124.20
Purchase #2	$46.29	12.589%	$52.1174	$52.12	$52.10	$52.10
Purchase #3	$50.86	11.144%	$56.5278	$56.53	$56.55	$56.50
Purchase #4	$67.91	7.257%	$72.8382	$72.84	$72.85	$72.80
Purchase #5	$250.28	8.342%	$271.1584	$271.16	$271.15	$271.20
Purchase #6	$210.72	4.509%	$220.2214	$220.22	$220.20	$220.20
Purchase #7	$57.58	7.573%	$61.9405	$61.94	$61.95	$61.90
7 purchase totals =	$793.90		$858.9576	$858.96	$858.95	$858.90