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	$182.88	9.845%	$200.8845	$200.88	$200.90	$200.90
Purchase #2	$179.48	9.496%	$196.5234	$196.52	$196.50	$196.50
Purchase #3	$84.81	7.188%	$90.9061	$90.91	$90.90	$90.90
Purchase #4	$46.68	12.144%	$52.3488	$52.35	$52.35	$52.30
Purchase #5	$124.85	3.445%	$129.1511	$129.15	$129.15	$129.20
Purchase #6	$61.47	4.689%	$64.3523	$64.35	$64.35	$64.40
Purchase #7	$88.86	5.412%	$93.6691	$93.67	$93.65	$93.70
7 purchase totals =	$769.03		$827.8353	$827.83	$827.80	$827.90