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	$118.74	10.754%	$131.5093	$131.51	$131.50	$131.50
Purchase #2	$23.90	7.252%	$25.6332	$25.63	$25.65	$25.60
Purchase #3	$213.89	12.483%	$240.5899	$240.59	$240.60	$240.60
Purchase #4	$115.59	3.601%	$119.7524	$119.75	$119.75	$119.80
Purchase #5	$76.92	4.220%	$80.166	$80.17	$80.15	$80.20
Purchase #6	$78.90	13.312%	$89.4032	$89.40	$89.40	$89.40
Purchase #7	$96.96	10.565%	$107.2038	$107.20	$107.20	$107.20
7 purchase totals =	$724.90		$794.2578	$794.25	$794.25	$794.30