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	$122.71	9.316%	$134.1417	$134.14	$134.15	$134.10
Purchase #2	$23.81	8.839%	$25.9146	$25.91	$25.90	$25.90
Purchase #3	$200.34	10.485%	$221.3456	$221.35	$221.35	$221.30
Purchase #4	$182.95	7.394%	$196.4773	$196.48	$196.50	$196.50
Purchase #5	$88.33	12.565%	$99.4287	$99.43	$99.45	$99.40
Purchase #6	$98.87	5.701%	$104.5066	$104.51	$104.50	$104.50
Purchase #7	$102.46	7.191%	$109.8279	$109.83	$109.85	$109.80
7 purchase totals =	$819.47		$891.6424	$891.65	$891.70	$891.50