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	$235.36	5.615%	$248.5755	$248.58	$248.60	$248.60
Purchase #2	$76.31	7.590%	$82.1019	$82.10	$82.10	$82.10
Purchase #3	$52.86	3.103%	$54.5002	$54.50	$54.50	$54.50
Purchase #4	$168.75	12.511%	$189.8623	$189.86	$189.85	$189.90
Purchase #5	$174.36	9.611%	$191.1177	$191.12	$191.10	$191.10
Purchase #6	$116.48	3.322%	$120.3495	$120.35	$120.35	$120.30
Purchase #7	$250.40	12.156%	$280.8386	$280.84	$280.85	$280.80
7 purchase totals =	$1,074.52		$1,167.3457	$1,167.35	$1,167.35	$1,167.30