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	$81.82	9.753%	$89.7999	$89.80	$89.80	$89.80
Purchase #2	$140.61	6.260%	$149.4122	$149.41	$149.40	$149.40
Purchase #3	$30.49	8.471%	$33.0728	$33.07	$33.05	$33.10
Purchase #4	$179.38	5.671%	$189.5526	$189.55	$189.55	$189.60
Purchase #5	$33.37	13.532%	$37.8856	$37.89	$37.90	$37.90
Purchase #6	$89.34	7.297%	$95.8591	$95.86	$95.85	$95.90
Purchase #7	$76.58	5.599%	$80.8677	$80.87	$80.85	$80.90
7 purchase totals =	$631.59		$676.4499	$676.45	$676.40	$676.60