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	$150.62	11.323%	$167.6747	$167.67	$167.65	$167.70
Purchase #2	$39.45	4.314%	$41.1519	$41.15	$41.15	$41.20
Purchase #3	$109.93	3.536%	$113.8171	$113.82	$113.80	$113.80
Purchase #4	$81.83	10.375%	$90.3199	$90.32	$90.30	$90.30
Purchase #5	$17.32	11.544%	$19.3194	$19.32	$19.30	$19.30
Purchase #6	$210.41	13.797%	$239.4403	$239.44	$239.45	$239.40
Purchase #7	$245.27	12.466%	$275.8454	$275.85	$275.85	$275.80
7 purchase totals =	$854.83		$947.5687	$947.57	$947.50	$947.50