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	$125.76	9.587%	$137.8166	$137.82	$137.80	$137.80
Purchase #2	$39.50	4.868%	$41.4229	$41.42	$41.40	$41.40
Purchase #3	$164.84	9.751%	$180.9135	$180.91	$180.90	$180.90
Purchase #4	$68.62	13.721%	$78.0354	$78.04	$78.05	$78.00
Purchase #5	$240.33	9.479%	$263.1109	$263.11	$263.10	$263.10
Purchase #6	$164.77	5.303%	$173.5078	$173.51	$173.50	$173.50
Purchase #7	$105.61	9.110%	$115.2311	$115.23	$115.25	$115.20
7 purchase totals =	$909.43		$990.0382	$990.04	$990.00	$989.90