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	$81.84	9.143%	$89.3226	$89.32	$89.30	$89.30
Purchase #2	$127.52	4.699%	$133.5122	$133.51	$133.50	$133.50
Purchase #3	$183.38	7.485%	$197.106	$197.11	$197.10	$197.10
Purchase #4	$139.45	3.640%	$144.526	$144.53	$144.55	$144.50
Purchase #5	$7.60	9.652%	$8.3336	$8.33	$8.35	$8.30
Purchase #6	$145.38	13.502%	$165.0092	$165.01	$165.00	$165.00
Purchase #7	$102.47	6.850%	$109.4892	$109.49	$109.50	$109.50
7 purchase totals =	$787.64		$847.2988	$847.30	$847.30	$847.20