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	$67.94	6.149%	$72.1176	$72.12	$72.10	$72.10
Purchase #2	$88.36	13.214%	$100.0359	$100.04	$100.05	$100.00
Purchase #3	$130.43	9.830%	$143.2513	$143.25	$143.25	$143.30
Purchase #4	$190.44	3.224%	$196.5798	$196.58	$196.60	$196.60
Purchase #5	$240.82	7.498%	$258.8767	$258.88	$258.90	$258.90
Purchase #6	$46.39	7.475%	$49.8577	$49.86	$49.85	$49.90
Purchase #7	$134.59	11.318%	$149.8229	$149.82	$149.80	$149.80
7 purchase totals =	$898.97		$970.5419	$970.55	$970.55	$970.60