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	$29.56	12.681%	$33.3085	$33.31	$33.30	$33.30
Purchase #2	$189.66	5.551%	$200.188	$200.19	$200.20	$200.20
Purchase #3	$107.31	5.215%	$112.9062	$112.91	$112.90	$112.90
Purchase #4	$106.56	4.289%	$111.1304	$111.13	$111.15	$111.10
Purchase #5	$51.57	9.688%	$56.5661	$56.57	$56.55	$56.60
Purchase #6	$116.71	3.576%	$120.8835	$120.88	$120.90	$120.90
Purchase #7	$41.33	12.174%	$46.3615	$46.36	$46.35	$46.40
7 purchase totals =	$642.70		$681.3442	$681.35	$681.35	$681.40