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	$76.47	3.859%	$79.421	$79.42	$79.40	$79.40
Purchase #2	$14.78	5.146%	$15.5406	$15.54	$15.55	$15.50
Purchase #3	$90.83	9.470%	$99.4316	$99.43	$99.45	$99.40
Purchase #4	$177.28	10.672%	$196.1993	$196.20	$196.20	$196.20
Purchase #5	$144.44	10.366%	$159.4127	$159.41	$159.40	$159.40
Purchase #6	$112.90	4.604%	$118.0979	$118.10	$118.10	$118.10
Purchase #7	$85.69	4.806%	$89.8083	$89.81	$89.80	$89.80
7 purchase totals =	$702.39		$757.9114	$757.91	$757.90	$757.80