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	$135.95	12.660%	$153.1613	$153.16	$153.15	$153.20
Purchase #2	$218.31	3.790%	$226.5839	$226.58	$226.60	$226.60
Purchase #3	$82.35	8.625%	$89.4527	$89.45	$89.45	$89.50
Purchase #4	$38.57	8.548%	$41.867	$41.87	$41.85	$41.90
Purchase #5	$93.61	6.159%	$99.3754	$99.38	$99.40	$99.40
Purchase #6	$88.54	6.210%	$94.0383	$94.04	$94.05	$94.00
Purchase #7	$247.58	8.676%	$269.06	$269.06	$269.05	$269.10
7 purchase totals =	$904.91		$973.5386	$973.54	$973.55	$973.70