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	$246.56	13.718%	$280.3831	$280.38	$280.40	$280.40
Purchase #2	$191.31	11.596%	$213.4943	$213.49	$213.50	$213.50
Purchase #3	$134.29	12.741%	$151.3999	$151.40	$151.40	$151.40
Purchase #4	$113.68	8.590%	$123.4451	$123.45	$123.45	$123.40
Purchase #5	$189.32	5.149%	$199.0681	$199.07	$199.05	$199.10
Purchase #6	$171.71	9.864%	$188.6475	$188.65	$188.65	$188.60
Purchase #7	$88.49	13.277%	$100.2388	$100.24	$100.25	$100.20
7 purchase totals =	$1,135.36		$1,256.6768	$1,256.68	$1,256.70	$1,256.60