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	$124.79	3.325%	$128.9393	$128.94	$128.95	$128.90
Purchase #2	$105.45	9.482%	$115.4488	$115.45	$115.45	$115.40
Purchase #3	$158.64	7.746%	$170.9283	$170.93	$170.95	$170.90
Purchase #4	$72.94	12.715%	$82.2143	$82.21	$82.20	$82.20
Purchase #5	$180.91	8.768%	$196.7722	$196.77	$196.75	$196.80
Purchase #6	$42.53	3.599%	$44.0607	$44.06	$44.05	$44.10
Purchase #7	$145.64	10.256%	$160.5768	$160.58	$160.60	$160.60
7 purchase totals =	$830.90		$898.9404	$898.94	$898.95	$898.90