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	$21.28	8.496%	$23.0879	$23.09	$23.10	$23.10
Purchase #2	$179.40	6.859%	$191.705	$191.71	$191.70	$191.70
Purchase #3	$75.70	8.716%	$82.298	$82.30	$82.30	$82.30
Purchase #4	$239.32	10.405%	$264.2212	$264.22	$264.20	$264.20
Purchase #5	$76.84	6.499%	$81.8338	$81.83	$81.85	$81.80
Purchase #6	$134.30	12.535%	$151.1345	$151.13	$151.15	$151.10
Purchase #7	$208.77	6.647%	$222.6469	$222.65	$222.65	$222.60
7 purchase totals =	$935.61		$1,016.9273	$1,016.93	$1,016.95	$1,016.80