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	$101.77	9.648%	$111.5888	$111.59	$111.60	$111.60
Purchase #2	$165.49	13.733%	$188.2167	$188.22	$188.20	$188.20
Purchase #3	$155.49	3.469%	$160.8839	$160.88	$160.90	$160.90
Purchase #4	$135.88	11.351%	$151.3037	$151.30	$151.30	$151.30
Purchase #5	$93.56	12.145%	$104.9229	$104.92	$104.90	$104.90
Purchase #6	$72.97	12.635%	$82.1898	$82.19	$82.20	$82.20
Purchase #7	$131.73	6.602%	$140.4268	$140.43	$140.45	$140.40
7 purchase totals =	$856.89		$939.5326	$939.53	$939.55	$939.50