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	$81.42	12.796%	$91.8385	$91.84	$91.85	$91.80
Purchase #2	$95.76	7.584%	$103.0224	$103.02	$103.00	$103.00
Purchase #3	$13.90	12.304%	$15.6103	$15.61	$15.60	$15.60
Purchase #4	$93.50	6.863%	$99.9169	$99.92	$99.90	$99.90
Purchase #5	$114.96	12.865%	$129.7496	$129.75	$129.75	$129.70
Purchase #6	$42.32	9.271%	$46.2435	$46.24	$46.25	$46.20
Purchase #7	$136.56	7.532%	$146.8457	$146.85	$146.85	$146.80
7 purchase totals =	$578.42		$633.2269	$633.23	$633.20	$633.00