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	$28.60	9.554%	$31.3324	$31.33	$31.35	$31.30
Purchase #2	$199.95	12.849%	$225.6416	$225.64	$225.65	$225.60
Purchase #3	$146.51	6.515%	$156.0551	$156.06	$156.05	$156.10
Purchase #4	$192.39	8.326%	$208.4084	$208.41	$208.40	$208.40
Purchase #5	$148.95	13.682%	$169.3293	$169.33	$169.35	$169.30
Purchase #6	$52.92	11.683%	$59.1026	$59.10	$59.10	$59.10
Purchase #7	$211.40	9.741%	$231.9925	$231.99	$232.00	$232.00
7 purchase totals =	$980.72		$1,081.8619	$1,081.86	$1,081.90	$1,081.80