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	$51.98	9.741%	$57.0434	$57.04	$57.05	$57.00
Purchase #2	$104.43	13.508%	$118.5364	$118.54	$118.55	$118.50
Purchase #3	$244.91	6.768%	$261.4855	$261.49	$261.50	$261.50
Purchase #4	$111.31	7.152%	$119.2709	$119.27	$119.25	$119.30
Purchase #5	$71.65	9.515%	$78.4675	$78.47	$78.45	$78.50
Purchase #6	$33.93	13.544%	$38.5255	$38.53	$38.55	$38.50
Purchase #7	$67.27	9.371%	$73.5739	$73.57	$73.55	$73.60
7 purchase totals =	$685.48		$746.9031	$746.91	$746.90	$746.90