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	$38.38	11.839%	$42.9238	$42.92	$42.90	$42.90
Purchase #2	$95.29	11.676%	$106.4161	$106.42	$106.40	$106.40
Purchase #3	$24.50	13.167%	$27.7259	$27.73	$27.75	$27.70
Purchase #4	$11.35	7.661%	$12.2195	$12.22	$12.20	$12.20
Purchase #5	$246.35	3.821%	$255.763	$255.76	$255.75	$255.80
Purchase #6	$17.32	6.397%	$18.428	$18.43	$18.45	$18.40
Purchase #7	$200.37	6.742%	$213.8789	$213.88	$213.90	$213.90
7 purchase totals =	$633.56		$677.3552	$677.36	$677.35	$677.30