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	$82.63	9.120%	$90.1659	$90.17	$90.15	$90.20
Purchase #2	$242.72	9.507%	$265.7954	$265.80	$265.80	$265.80
Purchase #3	$57.62	3.440%	$59.6021	$59.60	$59.60	$59.60
Purchase #4	$189.95	4.263%	$198.0476	$198.05	$198.05	$198.00
Purchase #5	$185.77	7.821%	$200.2991	$200.30	$200.30	$200.30
Purchase #6	$225.35	4.436%	$235.3465	$235.35	$235.35	$235.30
Purchase #7	$45.58	9.215%	$49.7802	$49.78	$49.80	$49.80
7 purchase totals =	$1,029.62		$1,099.0368	$1,099.05	$1,099.05	$1,099.00