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	$81.80	11.250%	$91.0025	$91.00	$91.00	$91.00
Purchase #2	$115.88	7.272%	$124.3068	$124.31	$124.30	$124.30
Purchase #3	$131.74	5.690%	$139.236	$139.24	$139.25	$139.20
Purchase #4	$154.57	13.140%	$174.8805	$174.88	$174.90	$174.90
Purchase #5	$119.79	12.647%	$134.9398	$134.94	$134.95	$134.90
Purchase #6	$111.81	10.694%	$123.767	$123.77	$123.75	$123.80
Purchase #7	$111.25	4.345%	$116.0838	$116.08	$116.10	$116.10
7 purchase totals =	$826.84		$904.2164	$904.22	$904.25	$904.20