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	$131.65	8.299%	$142.5756	$142.58	$142.60	$142.60
Purchase #2	$116.92	4.632%	$122.3357	$122.34	$122.35	$122.30
Purchase #3	$215.97	6.279%	$229.5308	$229.53	$229.55	$229.50
Purchase #4	$33.45	5.179%	$35.1824	$35.18	$35.20	$35.20
Purchase #5	$151.92	11.683%	$169.6688	$169.67	$169.65	$169.70
Purchase #6	$146.38	8.168%	$158.3363	$158.34	$158.35	$158.30
Purchase #7	$53.96	10.132%	$59.4272	$59.43	$59.45	$59.40
7 purchase totals =	$850.25		$917.0568	$917.07	$917.15	$917.00