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	$35.40	10.642%	$39.1673	$39.17	$39.15	$39.20
Purchase #2	$151.64	13.179%	$171.6246	$171.62	$171.60	$171.60
Purchase #3	$204.78	7.359%	$219.8498	$219.85	$219.85	$219.80
Purchase #4	$242.42	7.157%	$259.77	$259.77	$259.75	$259.80
Purchase #5	$173.40	3.559%	$179.5713	$179.57	$179.55	$179.60
Purchase #6	$119.35	3.796%	$123.8805	$123.88	$123.90	$123.90
Purchase #7	$28.37	7.522%	$30.504	$30.50	$30.50	$30.50
7 purchase totals =	$955.36		$1,024.3675	$1,024.36	$1,024.30	$1,024.40