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	$243.50	10.828%	$269.8662	$269.87	$269.85	$269.90
Purchase #2	$72.61	13.196%	$82.1916	$82.19	$82.20	$82.20
Purchase #3	$243.64	8.639%	$264.6881	$264.69	$264.70	$264.70
Purchase #4	$137.32	11.300%	$152.8372	$152.84	$152.85	$152.80
Purchase #5	$232.39	12.462%	$261.3504	$261.35	$261.35	$261.40
Purchase #6	$86.52	4.250%	$90.1971	$90.20	$90.20	$90.20
Purchase #7	$48.27	4.468%	$50.4267	$50.43	$50.45	$50.40
7 purchase totals =	$1,064.25		$1,171.5573	$1,171.57	$1,171.60	$1,171.60