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	$18.31	11.870%	$20.4834	$20.48	$20.50	$20.50
Purchase #2	$204.45	6.700%	$218.1482	$218.15	$218.15	$218.10
Purchase #3	$71.77	8.819%	$78.0994	$78.10	$78.10	$78.10
Purchase #4	$164.46	11.731%	$183.7528	$183.75	$183.75	$183.80
Purchase #5	$179.31	4.598%	$187.5547	$187.55	$187.55	$187.60
Purchase #6	$162.69	9.589%	$178.2903	$178.29	$178.30	$178.30
Purchase #7	$141.90	5.604%	$149.8521	$149.85	$149.85	$149.90
7 purchase totals =	$942.89		$1,016.1809	$1,016.17	$1,016.20	$1,016.30