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	$245.66	6.858%	$262.5074	$262.51	$262.50	$262.50
Purchase #2	$86.88	3.674%	$90.072	$90.07	$90.05	$90.10
Purchase #3	$38.46	4.636%	$40.243	$40.24	$40.25	$40.20
Purchase #4	$181.43	13.695%	$206.2768	$206.28	$206.30	$206.30
Purchase #5	$74.29	11.648%	$82.9433	$82.94	$82.95	$82.90
Purchase #6	$121.63	8.359%	$131.7971	$131.80	$131.80	$131.80
Purchase #7	$172.33	8.164%	$186.399	$186.40	$186.40	$186.40
7 purchase totals =	$920.68		$1,000.2386	$1,000.24	$1,000.25	$1,000.20