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	$94.78	6.458%	$100.9009	$100.90	$100.90	$100.90
Purchase #2	$31.76	6.795%	$33.9181	$33.92	$33.90	$33.90
Purchase #3	$36.66	13.801%	$41.7194	$41.72	$41.70	$41.70
Purchase #4	$149.59	6.868%	$159.8638	$159.86	$159.85	$159.90
Purchase #5	$47.32	6.743%	$50.5108	$50.51	$50.50	$50.50
Purchase #6	$120.83	5.360%	$127.3065	$127.31	$127.30	$127.30
Purchase #7	$143.55	10.465%	$158.5725	$158.57	$158.55	$158.60
7 purchase totals =	$624.49		$672.7920	$672.79	$672.70	$672.80