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	$89.86	10.494%	$99.2899	$99.29	$99.30	$99.30
Purchase #2	$32.79	8.751%	$35.6595	$35.66	$35.65	$35.70
Purchase #3	$115.79	6.753%	$123.6093	$123.61	$123.60	$123.60
Purchase #4	$159.31	13.673%	$181.0925	$181.09	$181.10	$181.10
Purchase #5	$117.39	7.794%	$126.5394	$126.54	$126.55	$126.50
Purchase #6	$162.45	11.552%	$181.2162	$181.22	$181.20	$181.20
Purchase #7	$234.66	11.452%	$261.5333	$261.53	$261.55	$261.50
7 purchase totals =	$912.25		$1,008.9401	$1,008.94	$1,008.95	$1,008.90