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	$24.97	11.384%	$27.8126	$27.81	$27.80	$27.80
Purchase #2	$176.28	7.215%	$188.9986	$189.00	$189.00	$189.00
Purchase #3	$198.93	11.654%	$222.1133	$222.11	$222.10	$222.10
Purchase #4	$34.34	13.128%	$38.8482	$38.85	$38.85	$38.80
Purchase #5	$176.84	11.147%	$196.5524	$196.55	$196.55	$196.60
Purchase #6	$237.92	7.271%	$255.2192	$255.22	$255.20	$255.20
Purchase #7	$106.73	11.416%	$118.9143	$118.91	$118.90	$118.90
7 purchase totals =	$956.01		$1,048.4586	$1,048.45	$1,048.40	$1,048.40