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	$155.60	6.303%	$165.4075	$165.41	$165.40	$165.40
Purchase #2	$99.35	7.617%	$106.9175	$106.92	$106.90	$106.90
Purchase #3	$233.73	9.752%	$256.5233	$256.52	$256.50	$256.50
Purchase #4	$94.40	7.156%	$101.1553	$101.16	$101.15	$101.20
Purchase #5	$114.57	11.192%	$127.3927	$127.39	$127.40	$127.40
Purchase #6	$38.69	8.701%	$42.0564	$42.06	$42.05	$42.10
Purchase #7	$191.60	3.406%	$198.1259	$198.13	$198.15	$198.10
7 purchase totals =	$927.94		$997.5786	$997.59	$997.55	$997.60