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	$64.42	10.519%	$71.1963	$71.20	$71.20	$71.20
Purchase #2	$122.84	13.471%	$139.3878	$139.39	$139.40	$139.40
Purchase #3	$89.53	11.784%	$100.0802	$100.08	$100.10	$100.10
Purchase #4	$125.46	12.116%	$140.6607	$140.66	$140.65	$140.70
Purchase #5	$160.46	9.510%	$175.7197	$175.72	$175.70	$175.70
Purchase #6	$25.35	9.772%	$27.8272	$27.83	$27.85	$27.80
Purchase #7	$35.73	10.380%	$39.4388	$39.44	$39.45	$39.40
7 purchase totals =	$623.79		$694.3107	$694.32	$694.35	$694.30