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	$123.29	8.871%	$134.2271	$134.23	$134.25	$134.20
Purchase #2	$33.63	12.620%	$37.8741	$37.87	$37.85	$37.90
Purchase #3	$177.35	12.782%	$200.0189	$200.02	$200.00	$200.00
Purchase #4	$7.46	5.102%	$7.8406	$7.84	$7.85	$7.80
Purchase #5	$50.66	7.525%	$54.4722	$54.47	$54.45	$54.50
Purchase #6	$51.27	12.421%	$57.6382	$57.64	$57.65	$57.60
Purchase #7	$137.39	4.410%	$143.4489	$143.45	$143.45	$143.40
7 purchase totals =	$581.05		$635.5200	$635.52	$635.50	$635.40