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	$237.59	6.656%	$253.404	$253.40	$253.40	$253.40
Purchase #2	$114.69	7.448%	$123.2321	$123.23	$123.25	$123.20
Purchase #3	$185.86	6.176%	$197.3387	$197.34	$197.35	$197.30
Purchase #4	$94.47	10.492%	$104.3818	$104.38	$104.40	$104.40
Purchase #5	$24.80	4.315%	$25.8701	$25.87	$25.85	$25.90
Purchase #6	$75.57	9.801%	$82.9766	$82.98	$83.00	$83.00
Purchase #7	$146.92	5.594%	$155.1387	$155.14	$155.15	$155.10
7 purchase totals =	$879.90		$942.3420	$942.34	$942.40	$942.30