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	$192.75	12.105%	$216.0824	$216.08	$216.10	$216.10
Purchase #2	$17.27	5.447%	$18.2107	$18.21	$18.20	$18.20
Purchase #3	$85.89	4.665%	$89.8968	$89.90	$89.90	$89.90
Purchase #4	$247.44	8.603%	$268.7273	$268.73	$268.75	$268.70
Purchase #5	$18.60	12.641%	$20.9512	$20.95	$20.95	$21.00
Purchase #6	$66.81	8.473%	$72.4708	$72.47	$72.45	$72.50
Purchase #7	$92.96	12.699%	$104.765	$104.77	$104.75	$104.80
7 purchase totals =	$721.72		$791.1042	$791.11	$791.10	$791.20