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	$50.62	10.544%	$55.9574	$55.96	$55.95	$56.00
Purchase #2	$32.78	3.359%	$33.8811	$33.88	$33.90	$33.90
Purchase #3	$228.60	11.597%	$255.1107	$255.11	$255.10	$255.10
Purchase #4	$131.96	13.872%	$150.2655	$150.27	$150.25	$150.30
Purchase #5	$84.51	7.344%	$90.7164	$90.72	$90.70	$90.70
Purchase #6	$104.82	3.396%	$108.3797	$108.38	$108.40	$108.40
Purchase #7	$175.38	12.351%	$197.0412	$197.04	$197.05	$197.00
7 purchase totals =	$808.67		$891.3520	$891.36	$891.35	$891.40