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	$146.59	12.824%	$165.3887	$165.39	$165.40	$165.40
Purchase #2	$79.77	3.221%	$82.3394	$82.34	$82.35	$82.30
Purchase #3	$144.90	4.372%	$151.235	$151.24	$151.25	$151.20
Purchase #4	$144.84	13.397%	$164.2442	$164.24	$164.25	$164.20
Purchase #5	$44.33	10.284%	$48.8889	$48.89	$48.90	$48.90
Purchase #6	$67.80	7.355%	$72.7867	$72.79	$72.80	$72.80
Purchase #7	$37.71	5.265%	$39.6954	$39.70	$39.70	$39.70
7 purchase totals =	$665.94		$724.5783	$724.59	$724.65	$724.50