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	$75.95	8.132%	$82.1263	$82.13	$82.15	$82.10
Purchase #2	$150.50	5.320%	$158.5066	$158.51	$158.50	$158.50
Purchase #3	$98.67	12.831%	$111.3303	$111.33	$111.35	$111.30
Purchase #4	$193.73	8.688%	$210.5613	$210.56	$210.55	$210.60
Purchase #5	$31.47	10.690%	$34.8341	$34.83	$34.85	$34.80
Purchase #6	$162.56	13.165%	$183.961	$183.96	$183.95	$184.00
Purchase #7	$57.82	9.607%	$63.3748	$63.37	$63.35	$63.40
7 purchase totals =	$770.70		$844.6944	$844.69	$844.70	$844.70