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	$38.62	10.328%	$42.6087	$42.61	$42.60	$42.60
Purchase #2	$216.72	12.648%	$244.1307	$244.13	$244.15	$244.10
Purchase #3	$243.38	10.474%	$268.8716	$268.87	$268.85	$268.90
Purchase #4	$110.50	5.193%	$116.2383	$116.24	$116.25	$116.20
Purchase #5	$29.32	4.243%	$30.564	$30.56	$30.55	$30.60
Purchase #6	$153.36	7.143%	$164.3145	$164.31	$164.30	$164.30
Purchase #7	$236.95	9.683%	$259.8939	$259.89	$259.90	$259.90
7 purchase totals =	$1,028.85		$1,126.6217	$1,126.61	$1,126.60	$1,126.60