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	$29.72	8.391%	$32.2138	$32.21	$32.20	$32.20
Purchase #2	$136.67	3.739%	$141.7801	$141.78	$141.80	$141.80
Purchase #3	$180.42	5.794%	$190.8735	$190.87	$190.85	$190.90
Purchase #4	$83.60	12.800%	$94.3008	$94.30	$94.30	$94.30
Purchase #5	$53.27	9.308%	$58.2284	$58.23	$58.25	$58.20
Purchase #6	$224.44	10.721%	$248.5022	$248.50	$248.50	$248.50
Purchase #7	$57.30	9.235%	$62.5917	$62.59	$62.60	$62.60
7 purchase totals =	$765.42		$828.4905	$828.48	$828.50	$828.50