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	$203.35	12.407%	$228.5796	$228.58	$228.60	$228.60
Purchase #2	$180.37	11.320%	$200.7879	$200.79	$200.80	$200.80
Purchase #3	$91.89	7.177%	$98.4849	$98.48	$98.50	$98.50
Purchase #4	$247.95	4.211%	$258.3912	$258.39	$258.40	$258.40
Purchase #5	$206.57	3.521%	$213.8433	$213.84	$213.85	$213.80
Purchase #6	$166.95	7.714%	$179.8285	$179.83	$179.85	$179.80
Purchase #7	$80.65	10.669%	$89.2545	$89.25	$89.25	$89.30
7 purchase totals =	$1,177.73		$1,269.1699	$1,269.16	$1,269.25	$1,269.20