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	$55.75	7.129%	$59.7244	$59.72	$59.70	$59.70
Purchase #2	$191.48	3.779%	$198.716	$198.72	$198.70	$198.70
Purchase #3	$149.77	13.183%	$169.5142	$169.51	$169.50	$169.50
Purchase #4	$122.83	8.586%	$133.3762	$133.38	$133.40	$133.40
Purchase #5	$59.64	11.536%	$66.5201	$66.52	$66.50	$66.50
Purchase #6	$237.27	11.590%	$264.7696	$264.77	$264.75	$264.80
Purchase #7	$72.57	12.201%	$81.4243	$81.42	$81.40	$81.40
7 purchase totals =	$889.31		$974.0448	$974.04	$973.95	$974.00