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	$235.80	3.588%	$244.2605	$244.26	$244.25	$244.30
Purchase #2	$108.82	6.400%	$115.7845	$115.78	$115.80	$115.80
Purchase #3	$129.32	12.761%	$145.8225	$145.82	$145.80	$145.80
Purchase #4	$166.72	8.512%	$180.9112	$180.91	$180.90	$180.90
Purchase #5	$80.57	12.471%	$90.6179	$90.62	$90.60	$90.60
Purchase #6	$108.95	3.442%	$112.7001	$112.70	$112.70	$112.70
Purchase #7	$91.43	9.143%	$99.7894	$99.79	$99.80	$99.80
7 purchase totals =	$921.61		$989.8861	$989.88	$989.85	$989.90