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	$249.56	5.589%	$263.5079	$263.51	$263.50	$263.50
Purchase #2	$109.83	7.275%	$117.8201	$117.82	$117.80	$117.80
Purchase #3	$116.71	9.209%	$127.4578	$127.46	$127.45	$127.50
Purchase #4	$131.57	10.578%	$145.4875	$145.49	$145.50	$145.50
Purchase #5	$153.47	5.755%	$162.3022	$162.30	$162.30	$162.30
Purchase #6	$117.47	4.150%	$122.345	$122.35	$122.35	$122.30
Purchase #7	$84.71	4.288%	$88.3424	$88.34	$88.35	$88.30
7 purchase totals =	$963.32		$1,027.2629	$1,027.27	$1,027.25	$1,027.20