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	$67.38	5.841%	$71.3157	$71.32	$71.30	$71.30
Purchase #2	$201.70	10.348%	$222.5719	$222.57	$222.55	$222.60
Purchase #3	$50.73	7.634%	$54.6027	$54.60	$54.60	$54.60
Purchase #4	$193.39	3.674%	$200.4951	$200.50	$200.50	$200.50
Purchase #5	$12.83	12.168%	$14.3912	$14.39	$14.40	$14.40
Purchase #6	$68.73	12.391%	$77.2463	$77.25	$77.25	$77.20
Purchase #7	$95.50	13.423%	$108.319	$108.32	$108.30	$108.30
7 purchase totals =	$690.26		$748.9419	$748.95	$748.90	$748.90