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	$63.32	6.532%	$67.4561	$67.46	$67.45	$67.50
Purchase #2	$105.41	5.687%	$111.4047	$111.40	$111.40	$111.40
Purchase #3	$158.72	4.158%	$165.3196	$165.32	$165.30	$165.30
Purchase #4	$184.76	7.325%	$198.2937	$198.29	$198.30	$198.30
Purchase #5	$142.92	8.866%	$155.5913	$155.59	$155.60	$155.60
Purchase #6	$128.77	10.591%	$142.408	$142.41	$142.40	$142.40
Purchase #7	$16.43	12.330%	$18.4558	$18.46	$18.45	$18.50
7 purchase totals =	$800.33		$858.9292	$858.93	$858.90	$859.00