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	$241.60	3.142%	$249.1911	$249.19	$249.20	$249.20
Purchase #2	$63.69	9.640%	$69.8297	$69.83	$69.85	$69.80
Purchase #3	$85.71	4.227%	$89.333	$89.33	$89.35	$89.30
Purchase #4	$166.79	4.592%	$174.449	$174.45	$174.45	$174.40
Purchase #5	$49.59	7.499%	$53.3088	$53.31	$53.30	$53.30
Purchase #6	$80.84	5.253%	$85.0865	$85.09	$85.10	$85.10
Purchase #7	$245.85	3.333%	$254.0442	$254.04	$254.05	$254.00
7 purchase totals =	$934.07		$975.2423	$975.24	$975.30	$975.10