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	$154.76	10.843%	$171.5406	$171.54	$171.55	$171.50
Purchase #2	$170.90	10.794%	$189.3469	$189.35	$189.35	$189.30
Purchase #3	$93.72	12.197%	$105.151	$105.15	$105.15	$105.20
Purchase #4	$119.55	10.368%	$131.9449	$131.94	$131.95	$131.90
Purchase #5	$83.81	4.537%	$87.6125	$87.61	$87.60	$87.60
Purchase #6	$132.84	5.274%	$139.846	$139.85	$139.85	$139.80
Purchase #7	$118.27	9.172%	$129.1177	$129.12	$129.10	$129.10
7 purchase totals =	$873.85		$954.5596	$954.56	$954.55	$954.40