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	$156.73	9.306%	$171.3153	$171.32	$171.30	$171.30
Purchase #2	$247.90	7.853%	$267.3676	$267.37	$267.35	$267.40
Purchase #3	$51.39	6.863%	$54.9169	$54.92	$54.90	$54.90
Purchase #4	$75.58	3.390%	$78.1422	$78.14	$78.15	$78.10
Purchase #5	$112.45	7.571%	$120.9636	$120.96	$120.95	$121.00
Purchase #6	$95.31	3.580%	$98.7221	$98.72	$98.70	$98.70
Purchase #7	$245.69	13.660%	$279.2513	$279.25	$279.25	$279.30
7 purchase totals =	$985.05		$1,070.6790	$1,070.68	$1,070.60	$1,070.70