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	$150.91	11.512%	$168.2828	$168.28	$168.30	$168.30
Purchase #2	$57.63	3.558%	$59.6805	$59.68	$59.70	$59.70
Purchase #3	$163.39	10.766%	$180.9806	$180.98	$181.00	$181.00
Purchase #4	$174.94	12.177%	$196.2424	$196.24	$196.25	$196.20
Purchase #5	$213.63	9.333%	$233.5681	$233.57	$233.55	$233.60
Purchase #6	$146.72	13.654%	$166.7531	$166.75	$166.75	$166.80
Purchase #7	$177.90	5.641%	$187.9353	$187.94	$187.95	$187.90
7 purchase totals =	$1,085.12		$1,193.4428	$1,193.44	$1,193.50	$1,193.50