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	$7.88	6.337%	$8.3794	$8.38	$8.40	$8.40
Purchase #2	$136.78	11.798%	$152.9173	$152.92	$152.90	$152.90
Purchase #3	$236.40	11.489%	$263.56	$263.56	$263.55	$263.60
Purchase #4	$111.81	5.165%	$117.585	$117.59	$117.60	$117.60
Purchase #5	$206.50	3.593%	$213.9195	$213.92	$213.90	$213.90
Purchase #6	$62.83	5.641%	$66.3742	$66.37	$66.35	$66.40
Purchase #7	$243.98	3.730%	$253.0805	$253.08	$253.10	$253.10
7 purchase totals =	$1,006.18		$1,075.8159	$1,075.82	$1,075.80	$1,075.90