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	$175.58	6.333%	$186.6995	$186.70	$186.70	$186.70
Purchase #2	$181.68	4.863%	$190.5151	$190.52	$190.50	$190.50
Purchase #3	$147.41	13.844%	$167.8174	$167.82	$167.80	$167.80
Purchase #4	$233.61	12.515%	$262.8463	$262.85	$262.85	$262.80
Purchase #5	$6.35	13.533%	$7.2093	$7.21	$7.20	$7.20
Purchase #6	$196.40	13.569%	$223.0495	$223.05	$223.05	$223.00
Purchase #7	$28.31	4.221%	$29.505	$29.51	$29.50	$29.50
7 purchase totals =	$969.34		$1,067.6421	$1,067.66	$1,067.60	$1,067.50