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	$97.59	11.786%	$109.092	$109.09	$109.10	$109.10
Purchase #2	$220.89	8.102%	$238.7865	$238.79	$238.80	$238.80
Purchase #3	$237.82	12.199%	$266.8317	$266.83	$266.85	$266.80
Purchase #4	$54.62	10.315%	$60.2541	$60.25	$60.25	$60.30
Purchase #5	$78.32	10.606%	$86.6266	$86.63	$86.65	$86.60
Purchase #6	$89.83	10.403%	$99.175	$99.18	$99.20	$99.20
Purchase #7	$18.54	5.335%	$19.5291	$19.53	$19.55	$19.50
7 purchase totals =	$797.61		$880.2950	$880.30	$880.40	$880.30