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	$122.94	6.112%	$130.4541	$130.45	$130.45	$130.50
Purchase #2	$115.80	12.842%	$130.671	$130.67	$130.65	$130.70
Purchase #3	$67.47	6.476%	$71.8394	$71.84	$71.85	$71.80
Purchase #4	$101.91	10.748%	$112.8633	$112.86	$112.85	$112.90
Purchase #5	$73.97	6.650%	$78.889	$78.89	$78.90	$78.90
Purchase #6	$162.82	5.632%	$171.99	$171.99	$172.00	$172.00
Purchase #7	$126.82	13.121%	$143.4601	$143.46	$143.45	$143.50
7 purchase totals =	$771.73		$840.1669	$840.16	$840.15	$840.30