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	$127.37	8.269%	$137.9022	$137.90	$137.90	$137.90
Purchase #2	$113.90	5.840%	$120.5518	$120.55	$120.55	$120.60
Purchase #3	$48.83	13.469%	$55.4069	$55.41	$55.40	$55.40
Purchase #4	$163.54	5.165%	$171.9868	$171.99	$172.00	$172.00
Purchase #5	$109.89	8.818%	$119.5801	$119.58	$119.60	$119.60
Purchase #6	$131.78	12.705%	$148.5226	$148.52	$148.50	$148.50
Purchase #7	$87.42	10.176%	$96.3159	$96.32	$96.30	$96.30
7 purchase totals =	$782.73		$850.2663	$850.27	$850.25	$850.30