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	$37.46	5.192%	$39.4049	$39.40	$39.40	$39.40
Purchase #2	$132.61	10.757%	$146.8749	$146.87	$146.85	$146.90
Purchase #3	$40.63	5.818%	$42.9939	$42.99	$43.00	$43.00
Purchase #4	$17.42	8.369%	$18.8779	$18.88	$18.90	$18.90
Purchase #5	$70.89	7.640%	$76.306	$76.31	$76.30	$76.30
Purchase #6	$131.53	11.716%	$146.9401	$146.94	$146.95	$146.90
Purchase #7	$95.49	6.223%	$101.4323	$101.43	$101.45	$101.40
7 purchase totals =	$526.03		$572.8300	$572.82	$572.85	$572.80