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	$17.37	3.453%	$17.9698	$17.97	$17.95	$18.00
Purchase #2	$225.43	7.391%	$242.0915	$242.09	$242.10	$242.10
Purchase #3	$141.71	8.532%	$153.8007	$153.80	$153.80	$153.80
Purchase #4	$136.47	11.842%	$152.6308	$152.63	$152.65	$152.60
Purchase #5	$148.37	13.782%	$168.8184	$168.82	$168.80	$168.80
Purchase #6	$144.92	3.721%	$150.3125	$150.31	$150.30	$150.30
Purchase #7	$180.25	11.432%	$200.8562	$200.86	$200.85	$200.90
7 purchase totals =	$994.52		$1,086.4799	$1,086.48	$1,086.45	$1,086.50