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	$135.31	13.745%	$153.9084	$153.91	$153.90	$153.90
Purchase #2	$211.29	9.743%	$231.876	$231.88	$231.90	$231.90
Purchase #3	$161.46	3.159%	$166.5605	$166.56	$166.55	$166.60
Purchase #4	$72.80	7.249%	$78.0773	$78.08	$78.10	$78.10
Purchase #5	$141.30	3.596%	$146.3811	$146.38	$146.40	$146.40
Purchase #6	$178.31	7.261%	$191.2571	$191.26	$191.25	$191.30
Purchase #7	$38.93	10.420%	$42.9865	$42.99	$43.00	$43.00
7 purchase totals =	$939.40		$1,011.0469	$1,011.06	$1,011.10	$1,011.20