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	$78.33	5.351%	$82.5214	$82.52	$82.50	$82.50
Purchase #2	$224.51	4.776%	$235.2326	$235.23	$235.25	$235.20
Purchase #3	$25.52	9.793%	$28.0192	$28.02	$28.00	$28.00
Purchase #4	$28.86	12.797%	$32.5532	$32.55	$32.55	$32.60
Purchase #5	$162.95	12.293%	$182.9814	$182.98	$183.00	$183.00
Purchase #6	$25.28	8.585%	$27.4503	$27.45	$27.45	$27.50
Purchase #7	$111.33	13.541%	$126.4052	$126.41	$126.40	$126.40
7 purchase totals =	$656.78		$715.1633	$715.16	$715.15	$715.20