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	$124.32	3.580%	$128.7707	$128.77	$128.75	$128.80
Purchase #2	$236.90	11.106%	$263.2101	$263.21	$263.20	$263.20
Purchase #3	$36.39	11.206%	$40.4679	$40.47	$40.45	$40.50
Purchase #4	$116.39	4.339%	$121.4402	$121.44	$121.45	$121.40
Purchase #5	$154.50	6.568%	$164.6476	$164.65	$164.65	$164.60
Purchase #6	$212.72	8.685%	$231.1947	$231.19	$231.20	$231.20
Purchase #7	$80.58	10.849%	$89.3221	$89.32	$89.30	$89.30
7 purchase totals =	$961.80		$1,039.0533	$1,039.05	$1,039.00	$1,039.00