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	$172.69	10.712%	$191.1886	$191.19	$191.20	$191.20
Purchase #2	$181.89	13.426%	$206.3106	$206.31	$206.30	$206.30
Purchase #3	$114.47	7.430%	$122.9751	$122.98	$123.00	$123.00
Purchase #4	$104.81	6.211%	$111.3197	$111.32	$111.30	$111.30
Purchase #5	$111.85	3.641%	$115.9225	$115.92	$115.90	$115.90
Purchase #6	$242.68	6.247%	$257.8402	$257.84	$257.85	$257.80
Purchase #7	$114.36	3.288%	$118.1202	$118.12	$118.10	$118.10
7 purchase totals =	$1,042.75		$1,123.6769	$1,123.68	$1,123.65	$1,123.60