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	$121.98	7.632%	$131.2895	$131.29	$131.30	$131.30
Purchase #2	$132.61	11.846%	$148.319	$148.32	$148.30	$148.30
Purchase #3	$248.55	12.645%	$279.9791	$279.98	$280.00	$280.00
Purchase #4	$82.45	5.289%	$86.8108	$86.81	$86.80	$86.80
Purchase #5	$225.31	5.470%	$237.6345	$237.63	$237.65	$237.60
Purchase #6	$155.41	12.188%	$174.3514	$174.35	$174.35	$174.40
Purchase #7	$224.72	11.340%	$250.2032	$250.20	$250.20	$250.20
7 purchase totals =	$1,191.03		$1,308.5875	$1,308.58	$1,308.60	$1,308.60