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	$104.87	10.265%	$115.6349	$115.63	$115.65	$115.60
Purchase #2	$100.59	9.104%	$109.7477	$109.75	$109.75	$109.70
Purchase #3	$139.81	11.627%	$156.0657	$156.07	$156.05	$156.10
Purchase #4	$40.27	5.602%	$42.5259	$42.53	$42.55	$42.50
Purchase #5	$7.46	6.571%	$7.9502	$7.95	$7.95	$8.00
Purchase #6	$145.25	5.270%	$152.9047	$152.90	$152.90	$152.90
Purchase #7	$93.48	6.496%	$99.5525	$99.55	$99.55	$99.60
7 purchase totals =	$631.73		$684.3816	$684.38	$684.40	$684.40