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	$55.73	6.778%	$59.5074	$59.51	$59.50	$59.50
Purchase #2	$169.34	3.414%	$175.1213	$175.12	$175.10	$175.10
Purchase #3	$17.64	13.800%	$20.0743	$20.07	$20.05	$20.10
Purchase #4	$113.40	9.243%	$123.8816	$123.88	$123.90	$123.90
Purchase #5	$52.48	11.819%	$58.6826	$58.68	$58.70	$58.70
Purchase #6	$37.88	13.435%	$42.9692	$42.97	$42.95	$43.00
Purchase #7	$225.85	6.306%	$240.0921	$240.09	$240.10	$240.10
7 purchase totals =	$672.32		$720.3285	$720.32	$720.30	$720.40