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	$99.86	6.669%	$106.5197	$106.52	$106.50	$106.50
Purchase #2	$80.88	6.666%	$86.2715	$86.27	$86.25	$86.30
Purchase #3	$198.71	9.626%	$217.8378	$217.84	$217.85	$217.80
Purchase #4	$153.30	11.144%	$170.3838	$170.38	$170.40	$170.40
Purchase #5	$113.72	8.613%	$123.5147	$123.51	$123.50	$123.50
Purchase #6	$37.94	11.291%	$42.2238	$42.22	$42.20	$42.20
Purchase #7	$204.79	9.166%	$223.5611	$223.56	$223.55	$223.60
7 purchase totals =	$889.20		$970.3124	$970.30	$970.25	$970.30