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	$79.27	11.146%	$88.1054	$88.11	$88.10	$88.10
Purchase #2	$79.86	8.362%	$86.5379	$86.54	$86.55	$86.50
Purchase #3	$117.50	13.545%	$133.4154	$133.42	$133.40	$133.40
Purchase #4	$49.47	9.870%	$54.3527	$54.35	$54.35	$54.40
Purchase #5	$94.64	3.724%	$98.1644	$98.16	$98.15	$98.20
Purchase #6	$98.89	4.534%	$103.3737	$103.37	$103.35	$103.40
Purchase #7	$69.29	12.730%	$78.1106	$78.11	$78.10	$78.10
7 purchase totals =	$588.92		$642.0601	$642.06	$642.00	$642.10