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	$149.98	6.740%	$160.0887	$160.09	$160.10	$160.10
Purchase #2	$65.76	11.513%	$73.3309	$73.33	$73.35	$73.30
Purchase #3	$43.45	5.360%	$45.7789	$45.78	$45.80	$45.80
Purchase #4	$13.34	9.675%	$14.6306	$14.63	$14.65	$14.60
Purchase #5	$80.97	10.220%	$89.2451	$89.25	$89.25	$89.20
Purchase #6	$169.59	3.627%	$175.741	$175.74	$175.75	$175.70
Purchase #7	$74.47	12.374%	$83.6849	$83.68	$83.70	$83.70
7 purchase totals =	$597.56		$642.5001	$642.50	$642.60	$642.40