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	$133.38	8.266%	$144.4052	$144.41	$144.40	$144.40
Purchase #2	$55.89	6.152%	$59.3284	$59.33	$59.35	$59.30
Purchase #3	$10.75	3.287%	$11.1034	$11.10	$11.10	$11.10
Purchase #4	$35.26	9.856%	$38.7352	$38.74	$38.75	$38.70
Purchase #5	$144.62	11.373%	$161.0676	$161.07	$161.05	$161.10
Purchase #6	$246.86	12.769%	$278.3816	$278.38	$278.40	$278.40
Purchase #7	$179.40	9.570%	$196.5686	$196.57	$196.55	$196.60
7 purchase totals =	$806.16		$889.5900	$889.60	$889.60	$889.60