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	$144.55	12.578%	$162.7315	$162.73	$162.75	$162.70
Purchase #2	$37.68	5.380%	$39.7072	$39.71	$39.70	$39.70
Purchase #3	$131.77	8.440%	$142.8914	$142.89	$142.90	$142.90
Purchase #4	$54.43	9.205%	$59.4403	$59.44	$59.45	$59.40
Purchase #5	$249.88	10.518%	$276.1624	$276.16	$276.15	$276.20
Purchase #6	$137.95	3.212%	$142.381	$142.38	$142.40	$142.40
Purchase #7	$147.90	7.481%	$158.9644	$158.96	$158.95	$159.00
7 purchase totals =	$904.16		$982.2782	$982.27	$982.30	$982.30