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	$142.30	12.726%	$160.4091	$160.41	$160.40	$160.40
Purchase #2	$25.89	13.337%	$29.3429	$29.34	$29.35	$29.30
Purchase #3	$100.37	3.189%	$103.5708	$103.57	$103.55	$103.60
Purchase #4	$173.49	8.535%	$188.2974	$188.30	$188.30	$188.30
Purchase #5	$37.52	13.808%	$42.7008	$42.70	$42.70	$42.70
Purchase #6	$78.94	4.521%	$82.5089	$82.51	$82.50	$82.50
Purchase #7	$223.59	9.861%	$245.6382	$245.64	$245.65	$245.60
7 purchase totals =	$782.10		$852.4681	$852.47	$852.45	$852.40