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	$91.91	9.385%	$100.5358	$100.54	$100.55	$100.50
Purchase #2	$131.81	7.270%	$141.3926	$141.39	$141.40	$141.40
Purchase #3	$156.63	5.320%	$164.9627	$164.96	$164.95	$165.00
Purchase #4	$235.65	5.552%	$248.7333	$248.73	$248.75	$248.70
Purchase #5	$146.53	13.175%	$165.8353	$165.84	$165.85	$165.80
Purchase #6	$180.76	4.636%	$189.14	$189.14	$189.15	$189.10
Purchase #7	$111.32	6.390%	$118.4333	$118.43	$118.45	$118.40
7 purchase totals =	$1,054.61		$1,129.0330	$1,129.03	$1,129.10	$1,128.90