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	$19.47	4.300%	$20.3072	$20.31	$20.30	$20.30
Purchase #2	$176.89	10.725%	$195.8615	$195.86	$195.85	$195.90
Purchase #3	$57.76	9.159%	$63.0502	$63.05	$63.05	$63.10
Purchase #4	$137.46	10.751%	$152.2383	$152.24	$152.25	$152.20
Purchase #5	$171.73	7.549%	$184.6939	$184.69	$184.70	$184.70
Purchase #6	$34.80	6.578%	$37.0891	$37.09	$37.10	$37.10
Purchase #7	$112.70	5.711%	$119.1363	$119.14	$119.15	$119.10
7 purchase totals =	$710.81		$772.3765	$772.38	$772.40	$772.40