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	$53.79	11.622%	$60.0415	$60.04	$60.05	$60.00
Purchase #2	$238.56	11.391%	$265.7344	$265.73	$265.75	$265.70
Purchase #3	$131.28	12.153%	$147.2345	$147.23	$147.25	$147.20
Purchase #4	$93.96	11.467%	$104.7344	$104.73	$104.75	$104.70
Purchase #5	$102.31	4.115%	$106.5201	$106.52	$106.50	$106.50
Purchase #6	$83.98	5.152%	$88.3066	$88.31	$88.30	$88.30
Purchase #7	$82.44	9.796%	$90.5158	$90.52	$90.50	$90.50
7 purchase totals =	$786.32		$863.0873	$863.08	$863.10	$862.90