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	$89.36	13.809%	$101.6997	$101.70	$101.70	$101.70
Purchase #2	$180.93	3.841%	$187.8795	$187.88	$187.90	$187.90
Purchase #3	$187.79	4.779%	$196.7645	$196.76	$196.75	$196.80
Purchase #4	$78.47	10.335%	$86.5799	$86.58	$86.60	$86.60
Purchase #5	$19.90	7.804%	$21.453	$21.45	$21.45	$21.50
Purchase #6	$161.69	6.769%	$172.6348	$172.63	$172.65	$172.60
Purchase #7	$135.32	3.272%	$139.7477	$139.75	$139.75	$139.70
7 purchase totals =	$853.46		$906.7591	$906.75	$906.80	$906.80