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	$211.32	4.217%	$220.2314	$220.23	$220.25	$220.20
Purchase #2	$97.54	6.533%	$103.9123	$103.91	$103.90	$103.90
Purchase #3	$232.50	9.590%	$254.7968	$254.80	$254.80	$254.80
Purchase #4	$149.47	4.412%	$156.0646	$156.06	$156.05	$156.10
Purchase #5	$115.49	7.328%	$123.9531	$123.95	$123.95	$124.00
Purchase #6	$81.85	9.680%	$89.7731	$89.77	$89.75	$89.80
Purchase #7	$122.40	12.703%	$137.9485	$137.95	$137.95	$137.90
7 purchase totals =	$1,010.57		$1,086.6798	$1,086.67	$1,086.65	$1,086.70