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	$66.83	6.572%	$71.2221	$71.22	$71.20	$71.20
Purchase #2	$152.31	13.484%	$172.8475	$172.85	$172.85	$172.80
Purchase #3	$49.61	5.110%	$52.1451	$52.15	$52.15	$52.10
Purchase #4	$169.59	10.469%	$187.3444	$187.34	$187.35	$187.30
Purchase #5	$82.93	6.293%	$88.1488	$88.15	$88.15	$88.10
Purchase #6	$132.70	11.633%	$148.137	$148.14	$148.15	$148.10
Purchase #7	$161.38	4.677%	$168.9277	$168.93	$168.95	$168.90
7 purchase totals =	$815.35		$888.7726	$888.78	$888.80	$888.50