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	$160.97	13.241%	$182.284	$182.28	$182.30	$182.30
Purchase #2	$205.76	9.749%	$225.8195	$225.82	$225.80	$225.80
Purchase #3	$35.95	5.244%	$37.8352	$37.84	$37.85	$37.80
Purchase #4	$85.72	5.259%	$90.228	$90.23	$90.25	$90.20
Purchase #5	$97.88	6.260%	$104.0073	$104.01	$104.00	$104.00
Purchase #6	$31.56	10.119%	$34.7536	$34.75	$34.75	$34.80
Purchase #7	$37.48	12.753%	$42.2598	$42.26	$42.25	$42.30
7 purchase totals =	$655.32		$717.1874	$717.19	$717.20	$717.20