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	$16.43	9.812%	$18.0421	$18.04	$18.05	$18.00
Purchase #2	$127.93	13.747%	$145.5165	$145.52	$145.50	$145.50
Purchase #3	$152.47	8.686%	$165.7135	$165.71	$165.70	$165.70
Purchase #4	$86.96	5.127%	$91.4184	$91.42	$91.40	$91.40
Purchase #5	$139.83	11.417%	$155.7944	$155.79	$155.80	$155.80
Purchase #6	$190.53	10.138%	$209.8459	$209.85	$209.85	$209.80
Purchase #7	$139.44	13.747%	$158.6088	$158.61	$158.60	$158.60
7 purchase totals =	$853.59		$944.9396	$944.94	$944.90	$944.80