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	$92.60	7.538%	$99.5802	$99.58	$99.60	$99.60
Purchase #2	$146.92	6.798%	$156.9076	$156.91	$156.90	$156.90
Purchase #3	$32.83	3.356%	$33.9318	$33.93	$33.95	$33.90
Purchase #4	$50.40	12.351%	$56.6249	$56.62	$56.60	$56.60
Purchase #5	$151.38	6.328%	$160.9593	$160.96	$160.95	$161.00
Purchase #6	$92.86	12.726%	$104.6774	$104.68	$104.70	$104.70
Purchase #7	$212.84	5.836%	$225.2613	$225.26	$225.25	$225.30
7 purchase totals =	$779.83		$837.9425	$837.94	$837.95	$838.00