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	$156.86	8.833%	$170.7154	$170.72	$170.70	$170.70
Purchase #2	$38.51	10.712%	$42.6352	$42.64	$42.65	$42.60
Purchase #3	$232.75	13.679%	$264.5879	$264.59	$264.60	$264.60
Purchase #4	$36.71	11.558%	$40.9529	$40.95	$40.95	$41.00
Purchase #5	$67.62	12.820%	$76.2889	$76.29	$76.30	$76.30
Purchase #6	$87.78	13.674%	$99.783	$99.78	$99.80	$99.80
Purchase #7	$85.87	9.297%	$93.8533	$93.85	$93.85	$93.90
7 purchase totals =	$706.10		$788.8166	$788.82	$788.85	$788.90