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	$120.78	5.841%	$127.8348	$127.83	$127.85	$127.80
Purchase #2	$63.41	10.609%	$70.1372	$70.14	$70.15	$70.10
Purchase #3	$34.36	11.187%	$38.2039	$38.20	$38.20	$38.20
Purchase #4	$135.92	4.165%	$141.5811	$141.58	$141.60	$141.60
Purchase #5	$78.83	10.244%	$86.9053	$86.91	$86.90	$86.90
Purchase #6	$210.46	12.104%	$235.9341	$235.93	$235.95	$235.90
Purchase #7	$98.64	11.438%	$109.9224	$109.92	$109.90	$109.90
7 purchase totals =	$742.40		$810.5188	$810.51	$810.55	$810.40