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	$157.38	13.428%	$178.513	$178.51	$178.50	$178.50
Purchase #2	$213.59	9.285%	$233.4218	$233.42	$233.40	$233.40
Purchase #3	$178.29	6.489%	$189.8592	$189.86	$189.85	$189.90
Purchase #4	$67.28	9.846%	$73.9044	$73.90	$73.90	$73.90
Purchase #5	$219.61	4.747%	$230.0349	$230.03	$230.05	$230.00
Purchase #6	$61.89	9.213%	$67.5919	$67.59	$67.60	$67.60
Purchase #7	$23.81	12.810%	$26.8601	$26.86	$26.85	$26.90
7 purchase totals =	$921.85		$1,000.1853	$1,000.17	$1,000.15	$1,000.20