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	$178.29	3.233%	$184.0541	$184.05	$184.05	$184.10
Purchase #2	$137.61	10.376%	$151.8884	$151.89	$151.90	$151.90
Purchase #3	$103.56	12.520%	$116.5257	$116.53	$116.55	$116.50
Purchase #4	$154.88	8.330%	$167.7815	$167.78	$167.80	$167.80
Purchase #5	$216.31	8.549%	$234.8023	$234.80	$234.80	$234.80
Purchase #6	$36.62	10.428%	$40.4387	$40.44	$40.45	$40.40
Purchase #7	$113.45	13.129%	$128.3449	$128.34	$128.35	$128.30
7 purchase totals =	$940.72		$1,023.8356	$1,023.83	$1,023.90	$1,023.80