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	$30.57	10.568%	$33.8006	$33.80	$33.80	$33.80
Purchase #2	$63.77	11.709%	$71.2368	$71.24	$71.25	$71.20
Purchase #3	$118.92	6.213%	$126.3085	$126.31	$126.30	$126.30
Purchase #4	$247.31	10.705%	$273.7845	$273.78	$273.80	$273.80
Purchase #5	$104.47	8.616%	$113.4711	$113.47	$113.45	$113.50
Purchase #6	$123.52	7.678%	$133.0039	$133.00	$133.00	$133.00
Purchase #7	$249.66	7.475%	$268.3221	$268.32	$268.30	$268.30
7 purchase totals =	$938.22		$1,019.9275	$1,019.92	$1,019.90	$1,019.90