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	$93.50	6.836%	$99.8917	$99.89	$99.90	$99.90
Purchase #2	$133.76	6.648%	$142.6524	$142.65	$142.65	$142.70
Purchase #3	$186.69	6.152%	$198.1752	$198.18	$198.20	$198.20
Purchase #4	$84.93	8.360%	$92.0301	$92.03	$92.05	$92.00
Purchase #5	$236.45	10.453%	$261.1661	$261.17	$261.15	$261.20
Purchase #6	$108.25	4.226%	$112.8246	$112.82	$112.80	$112.80
Purchase #7	$127.27	11.395%	$141.7724	$141.77	$141.75	$141.80
7 purchase totals =	$970.85		$1,048.5125	$1,048.51	$1,048.50	$1,048.60