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	$90.61	9.818%	$99.5061	$99.51	$99.50	$99.50
Purchase #2	$62.31	10.358%	$68.7641	$68.76	$68.75	$68.80
Purchase #3	$112.35	3.454%	$116.2306	$116.23	$116.25	$116.20
Purchase #4	$131.98	9.538%	$144.5683	$144.57	$144.55	$144.60
Purchase #5	$199.61	11.713%	$222.9903	$222.99	$223.00	$223.00
Purchase #6	$228.97	4.314%	$238.8478	$238.85	$238.85	$238.80
Purchase #7	$151.67	12.502%	$170.6318	$170.63	$170.65	$170.60
7 purchase totals =	$977.50		$1,061.5390	$1,061.54	$1,061.55	$1,061.50