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	$24.97	13.202%	$28.2665	$28.27	$28.25	$28.30
Purchase #2	$129.36	10.492%	$142.9325	$142.93	$142.95	$142.90
Purchase #3	$112.92	12.609%	$127.1581	$127.16	$127.15	$127.20
Purchase #4	$199.63	8.812%	$217.2214	$217.22	$217.20	$217.20
Purchase #5	$65.69	8.732%	$71.4261	$71.43	$71.45	$71.40
Purchase #6	$212.51	13.570%	$241.3476	$241.35	$241.35	$241.30
Purchase #7	$104.73	7.613%	$112.7031	$112.70	$112.70	$112.70
7 purchase totals =	$849.81		$941.0553	$941.06	$941.05	$941.00