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	$100.53	10.311%	$110.8956	$110.90	$110.90	$110.90
Purchase #2	$85.32	7.769%	$91.9485	$91.95	$91.95	$91.90
Purchase #3	$94.54	6.283%	$100.4799	$100.48	$100.50	$100.50
Purchase #4	$58.73	6.427%	$62.5046	$62.50	$62.50	$62.50
Purchase #5	$30.77	7.467%	$33.0676	$33.07	$33.05	$33.10
Purchase #6	$132.84	8.803%	$144.5339	$144.53	$144.55	$144.50
Purchase #7	$115.29	11.758%	$128.8458	$128.85	$128.85	$128.80
7 purchase totals =	$618.02		$672.2759	$672.28	$672.30	$672.20