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	$226.49	12.336%	$254.4298	$254.43	$254.45	$254.40
Purchase #2	$125.31	6.268%	$133.1644	$133.16	$133.15	$133.20
Purchase #3	$250.39	3.513%	$259.1862	$259.19	$259.20	$259.20
Purchase #4	$199.82	9.146%	$218.0955	$218.10	$218.10	$218.10
Purchase #5	$31.52	7.415%	$33.8572	$33.86	$33.85	$33.90
Purchase #6	$18.59	13.258%	$21.0547	$21.05	$21.05	$21.10
Purchase #7	$85.49	12.636%	$96.2925	$96.29	$96.30	$96.30
7 purchase totals =	$937.61		$1,016.0803	$1,016.08	$1,016.10	$1,016.20