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	$138.68	12.138%	$155.513	$155.51	$155.50	$155.50
Purchase #2	$197.88	11.435%	$220.5076	$220.51	$220.50	$220.50
Purchase #3	$40.81	10.595%	$45.1338	$45.13	$45.15	$45.10
Purchase #4	$128.65	11.873%	$143.9246	$143.92	$143.90	$143.90
Purchase #5	$218.72	7.773%	$235.7211	$235.72	$235.70	$235.70
Purchase #6	$168.73	12.522%	$189.8584	$189.86	$189.85	$189.90
Purchase #7	$71.27	7.777%	$76.8127	$76.81	$76.80	$76.80
7 purchase totals =	$964.74		$1,067.4712	$1,067.46	$1,067.40	$1,067.40