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	$38.71	11.112%	$43.0115	$43.01	$43.00	$43.00
Purchase #2	$131.99	10.546%	$145.9097	$145.91	$145.90	$145.90
Purchase #3	$154.52	10.849%	$171.2839	$171.28	$171.30	$171.30
Purchase #4	$135.78	11.301%	$151.1245	$151.12	$151.10	$151.10
Purchase #5	$230.82	12.269%	$259.1393	$259.14	$259.15	$259.10
Purchase #6	$91.62	13.179%	$103.6946	$103.69	$103.70	$103.70
Purchase #7	$156.25	3.471%	$161.6734	$161.67	$161.65	$161.70
7 purchase totals =	$939.69		$1,035.8369	$1,035.82	$1,035.80	$1,035.80