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	$31.70	4.114%	$33.0041	$33.00	$33.00	$33.00
Purchase #2	$123.37	4.211%	$128.5651	$128.57	$128.55	$128.60
Purchase #3	$68.45	12.342%	$76.8981	$76.90	$76.90	$76.90
Purchase #4	$248.54	5.330%	$261.7872	$261.79	$261.80	$261.80
Purchase #5	$248.39	10.767%	$275.1342	$275.13	$275.15	$275.10
Purchase #6	$60.80	8.394%	$65.9036	$65.90	$65.90	$65.90
Purchase #7	$41.35	3.443%	$42.7737	$42.77	$42.75	$42.80
7 purchase totals =	$822.60		$884.0660	$884.06	$884.05	$884.10