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	$167.97	10.607%	$185.7866	$185.79	$185.80	$185.80
Purchase #2	$135.47	5.532%	$142.9642	$142.96	$142.95	$143.00
Purchase #3	$188.68	12.634%	$212.5178	$212.52	$212.50	$212.50
Purchase #4	$32.31	10.196%	$35.6043	$35.60	$35.60	$35.60
Purchase #5	$79.61	8.451%	$86.3378	$86.34	$86.35	$86.30
Purchase #6	$183.89	13.438%	$208.6011	$208.60	$208.60	$208.60
Purchase #7	$152.72	9.676%	$167.4972	$167.50	$167.50	$167.50
7 purchase totals =	$940.65		$1,039.3090	$1,039.31	$1,039.30	$1,039.30