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	$31.86	6.600%	$33.9628	$33.96	$33.95	$34.00
Purchase #2	$204.50	13.159%	$231.4102	$231.41	$231.40	$231.40
Purchase #3	$169.49	9.544%	$185.6661	$185.67	$185.65	$185.70
Purchase #4	$98.82	10.507%	$109.203	$109.20	$109.20	$109.20
Purchase #5	$51.52	10.235%	$56.7931	$56.79	$56.80	$56.80
Purchase #6	$99.39	5.229%	$104.5871	$104.59	$104.60	$104.60
Purchase #7	$123.46	12.223%	$138.5505	$138.55	$138.55	$138.60
7 purchase totals =	$779.04		$860.1728	$860.17	$860.15	$860.30