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	$78.59	13.461%	$89.169	$89.17	$89.15	$89.20
Purchase #2	$170.55	10.683%	$188.7699	$188.77	$188.75	$188.80
Purchase #3	$239.59	11.489%	$267.1165	$267.12	$267.10	$267.10
Purchase #4	$72.85	11.455%	$81.195	$81.20	$81.20	$81.20
Purchase #5	$245.88	5.615%	$259.6862	$259.69	$259.70	$259.70
Purchase #6	$112.55	13.220%	$127.4291	$127.43	$127.45	$127.40
Purchase #7	$159.64	12.618%	$179.7834	$179.78	$179.80	$179.80
7 purchase totals =	$1,079.65		$1,193.1491	$1,193.16	$1,193.15	$1,193.20