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	$113.38	6.550%	$120.8064	$120.81	$120.80	$120.80
Purchase #2	$73.45	12.355%	$82.5247	$82.52	$82.50	$82.50
Purchase #3	$53.51	4.441%	$55.8864	$55.89	$55.90	$55.90
Purchase #4	$240.51	13.565%	$273.1352	$273.14	$273.15	$273.10
Purchase #5	$46.67	3.700%	$48.3968	$48.40	$48.40	$48.40
Purchase #6	$183.67	12.106%	$205.9051	$205.91	$205.90	$205.90
Purchase #7	$160.29	3.458%	$165.8328	$165.83	$165.85	$165.80
7 purchase totals =	$871.48		$952.4874	$952.50	$952.50	$952.40