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	$72.29	11.321%	$80.474	$80.47	$80.45	$80.50
Purchase #2	$123.97	10.618%	$137.1331	$137.13	$137.15	$137.10
Purchase #3	$168.85	7.592%	$181.6691	$181.67	$181.65	$181.70
Purchase #4	$111.93	5.459%	$118.0403	$118.04	$118.05	$118.00
Purchase #5	$39.90	10.228%	$43.981	$43.98	$44.00	$44.00
Purchase #6	$35.84	7.188%	$38.4162	$38.42	$38.40	$38.40
Purchase #7	$118.47	4.457%	$123.7502	$123.75	$123.75	$123.80
7 purchase totals =	$671.25		$723.4639	$723.46	$723.45	$723.50