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	$223.76	7.367%	$240.2444	$240.24	$240.25	$240.20
Purchase #2	$181.61	10.522%	$200.719	$200.72	$200.70	$200.70
Purchase #3	$184.66	13.352%	$209.3158	$209.32	$209.30	$209.30
Purchase #4	$117.89	9.819%	$129.4656	$129.47	$129.45	$129.50
Purchase #5	$141.92	3.558%	$146.9695	$146.97	$146.95	$147.00
Purchase #6	$82.43	12.644%	$92.8524	$92.85	$92.85	$92.90
Purchase #7	$32.79	9.266%	$35.8283	$35.83	$35.85	$35.80
7 purchase totals =	$965.06		$1,055.3950	$1,055.40	$1,055.35	$1,055.40