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	$230.71	12.446%	$259.4242	$259.42	$259.40	$259.40
Purchase #2	$104.37	7.538%	$112.2374	$112.24	$112.25	$112.20
Purchase #3	$117.82	8.837%	$128.2318	$128.23	$128.25	$128.20
Purchase #4	$54.51	12.490%	$61.3183	$61.32	$61.30	$61.30
Purchase #5	$240.71	10.262%	$265.4117	$265.41	$265.40	$265.40
Purchase #6	$141.56	5.850%	$149.8413	$149.84	$149.85	$149.80
Purchase #7	$41.70	13.301%	$47.2465	$47.25	$47.25	$47.20
7 purchase totals =	$931.38		$1,023.7112	$1,023.71	$1,023.70	$1,023.50