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	$34.59	12.551%	$38.9314	$38.93	$38.95	$38.90
Purchase #2	$42.66	6.844%	$45.5797	$45.58	$45.60	$45.60
Purchase #3	$87.33	13.107%	$98.7763	$98.78	$98.80	$98.80
Purchase #4	$28.99	13.492%	$32.9013	$32.90	$32.90	$32.90
Purchase #5	$106.46	12.648%	$119.9251	$119.93	$119.95	$119.90
Purchase #6	$139.80	6.155%	$148.4047	$148.40	$148.40	$148.40
Purchase #7	$199.56	7.231%	$213.9902	$213.99	$214.00	$214.00
7 purchase totals =	$639.39		$698.5087	$698.51	$698.60	$698.50